There's one civilization that I have not yet covered in my Brave New World strategies series that did receive an explicit rewrite of its unique national ability. I haven't covered them yet because that rewrite isn't so much a change to their ability, as it is really just a clarification that the ability applies to the new rules. The Iroquois civilization led by Chief Hiawatha has an ability that explicitly utilizes the expansion's trade route mechanics. The Iroquois are another civilization (like India) that receives a lot of hate from the Civ V gaming community due to some supposedly lackluster, highly-situational uniques. This strategy will focus on utilizing those uniques when they are beneficial, and on compensating for their downfalls and limitations.
Very little is known about the early history of Iroquoian people prior to the arrival of Europeans in the Americas. The Native American tribes had no written language, and their histories were passed down through oral tradition. According to that tradition, a great Peacemaker united the eastern Great Lakes tribes of the Mohawk, Oneida, Onandaga, Cayauga, and Seneca sometime between the 12th and 15th centuries. Other tribes would later join the confederacy, including some that were displaced from their native lands by European settlers. Iroquois culture was matrilineal, meaning that children were born into the mother's family, and women had a great deal of influence in the politics of the tribes. The Iroquois Confederacy utilized a representative system in which each tribe appointed a number of chiefs (based on relative population of the respective tribes) to serve on a council. There was both a council of male chiefs, and also a council of clan mothers that both had roughly equal authority.
Hiawatha is a near-mythical figure in Iroquois history. He was a follower of the Great Peacemaker, who traveled between the various tribes of the region preaching a prophecy of a strong alliance uniting all the tribes of the Great Lakes region in peace. Hiawatha, along with the Peacemaker, effectively founded the Iroquois Confederacy using his skills as an orator (and, in some traditions, magic) to convince the various tribes to join. According to oral tradition, the Seneca resisted the alliance, leading to a confrontation that was stopped when the sun miraculously went dark, turning day into night. This supposed solar eclipse lead the Seneca to put down their arms and commit themselves to the alliance.
Iroquois uniques in Civilization V: Brave New World
The Iroquois are one of the few civilizations that have highly situation - but non-naval - uniques, as well as one of the few civilizations that has a unique that presents an explicit and obvious liability. They require that the Iroquois have plenty of forest tiles in their territory. Leveraging these uniques when they are advantageous, and finding ways to offset their drawbacks in unfavorable conditions, is key to being successful with the Iroquois.
The Great Warpath
"Units move through Forest and Jungle in friendly territory as if they were Roads. These tiles can be used to establish City Connections upon researching The Wheel. Caravans move along Forest and Jungle as if they were Roads."
Plopping your Iroquois Nation within a large expanse of forest or jungle is required in order to utilize the Iroquois' Great Warpath ability, and you'll want your borders to encompass as much forest and jungle as possible in order to allow rapid movement of your units within your territory. Not having to build roads to facilitate movement and connect cities can save quite a bit of maintenance costs, allowing Iroquois gold to be spent on other endeavors such as paying maintenance for more units, bribing city states, trade deals, and so on. It can also free up a trade route to be used domestically for food or production shipments. These caravans will also have their range extended by forests, allowing them to reach more distant trade partners.
This ability also applies to friendly territory, so your units can also use open borders agreements and friendly city state territory to further increase their speed. The Iroquois mobility in friendly forests and jungles (and the Mohawk's combat modifier) can make Iroquois an excellent ally if you find yourself being invaded by a common enemy. Iroquois units can also be used to quickly maneuver through friendly or allied city state territory (if they have jungles or forests) to help defend them from invasion.
You must research The Wheel before forests can provide city connections.
Another key (but un-documented) advantage of Great Warpath is that forests also act as bridges prior to researching engineering. Iroquois units starting in a forest in friendly territory can cross a river without ending their movement! This enhanced mobility can be very useful in defending yourself from early barbarian rushes and for quickly moving your workers to resource tiles.
Since the ability only applies within your and friendly territory, you may still have to build roads if your cities are spread out so that their are gaps in your cultural borders between them. Once your borders expand to envelop forested tiles in between the cities, then you can feel free to delete the roads if you wish. You also can't ignore the wheel technology, since researching it is necessary to activate city connections via Great Warpath. When you research Railroad, your forest-connected cities will automatically receive the railroad production bonus; however, the movement speed of units does not increase unless you explicitly build rail.
Caravans can use forests and jungle as roads even in neutral territory, which can greatly increase their range and allow access to more distant (and hopefully profitable) trade routes.
Game Info: "Strong, front-line land Unit of the Classical Era. Only the Iroquois may build it. This Unit receives a major bonus when fighting on Forest and Jungle, unlike the Swordsman which it replaces."
Civilopedia Strategy: "The Mohawk Warrior is the Iroquoian unique unit, replacing the Swordsman. As powerful as the Swordsman in Clear or Hilly terrain, the Mohawk Warrior receives a significant combat bonus in Forest and Jungle. Also, unlike the Swordsman, it does not require Iron to build."
Requirements: Iron Working, and standard unit maintenance (same as Swordsman).
Obsoleted: Gunpowder technology, Upgrades to: Longswordsman (same as Swordsman).
Cost: 75 Production | 150 Faith | 270 Gold (same as Swordsman).
Attack Type: Melee, Combat Class: melee, Combat Strength: 14 (same as Swordsman).
Movement Speed: 2 (same as Swordsman).
Bonus(es): 33% combat bonus in forest and jungle.
Mohawk Warriors have the same base combat strength and movement as the swordsman that they replace. Their sole enhancement is that they receive an automatic 33% combat bonus in forest and jungles. Their primary benefit is actually what they do not have compared to the swordsman: which is that they do not require iron. Iroquois don't need to worry about acquiring iron until researching steel in the late middle ages.
Even after researching steel, the Mohawk does not become obsolete until gunpowder. This allows Iroquois to continue producing Mohawk Warriors and upgrade them to longswords and muskets that retain the 33% forest and jungle bonus. Don't bother building new longswords. Build Mohawks instead, and upgrade them to longswords. If you're short on iron, you can continue to produce Mohawks, upgrade your longswords into muskets to free up your iron supply, then upgrade your new Mohawks into longswords and muskets.
Mohawk Warriors are fast and dangerous in forests and jungles, especially if promoted with Drill.
They can even stand up against dangerous classical units like the Roman Legion!
With the combination of the Iroquois Great Warpath ability and the Mohawk's forest and jungle combat bonus, the unit can actually be an exceptionally fast and effective defensive unit. If your land is dominated by forests, then the Mohawk will be able to rapidly deploy to virtually any tile within or adjacent to your territory and receive a combat bonus against enemy units that try to hide in the forests or jungles. If your Mohawks fortify in the forest or jungle, then they'll receive the terrain defensive modifier in addition to their base forest and jungle modifier for a total of 58% defense (total of 83% if also on a hill). Forts can also be built on top of forests, and a stock Mohawk fortified within a fort on a forested hill receives a cummulative 133% defense modifier (and the attacker can receive a -20% penalty if you're also across a river). Taking Drill line of promotions will further buff your combat potential within forests and jungles.
Game Info: "+1 Production from each worked Forest tile."
Civilopedia Strategy: "The Longhouse is the Iroquois unique building, replacing the Workshop. It increases the city's Production output for each forest within the city's radius."
Requirements: Metal Casting technology, 2 gold per turn maintenance.
Cost: 100 Production (-20 from Workshop).
Effects: +2 production, +1 production for each worked forest tile in the city.
Does not have the Workshop's +10% production bonus..
Specialists: provides 1 engineer specialist slot.
The Longhouse is one of the few uniques in the game that can actually be considered inferior to the building that it replaces, due to the fact that it does not receive the automatic +10% production that the workshop provides. This is supposed to be offset by the additional production that the building applies to all worked forest tiles, but whether or not you can benefit from that is dependent on the map and your specific needs. If your city has a lot of forests, and you have enough food to work them, then the Longhouse will make that city very productive; if you don't have any forest, then it isn't even as good as a windmill. You generally only need to work 2 or 3 forests in a city in order for the Longhouse to become better than a Workshop. It's also important to note that the Longhouse does not buff jungles! The other two Iroquois uniques work in jungles, but not the Longhouse!
Longhouses may not be worthwhile for all cities.
Unlike the Celts' Druidic Lore ability, the Longhouse does not require that the forest be unimproved. You are free to build lumbermills, trade posts, roads, and forts on your forest tiles and will still benefit from the Longhouse's ability (in addition to the Great Warpath ability and the Mohawk's combat modifier). Just don't cut them down unless you really need to.
Another small compensation is that the Longhouse is actually 20 hammers (on standard game speed) less expensive than the workshop, making it 16.7% cheaper to build. It can generally be built a couple turns sooner than a workshop on standard game speed, giving you slightly quicker access to the engineer specialist and ability to ship production to other cities.
Strategies for following Hiawatha's Great Warpath
Starting in or adjacent to a large stretch of forest is essential for the Iroquois. Starting in jungle is OK too, but not as good, since it will limit or nullify the effectiveness of your Longhouse. Explore the forests quickly and thoroughly with a scout in order to find good city locations that have access to fresh water and resources. Adopting Tradition is highly recommended, as it will grant faster border growth, allowing you to claim more forest tiles faster.
When exploring forests, you'll specifically want to look for camp resources located within forests, since camps won't require that you cut down the underlying forest. Forests generally lack good food yield, so finding sources of food is very important
. Put priority on settling near deer
if you can find them, so that you can benefit from building Granaries
in your cities. Settling along rivers will also allow you to build Watermills
for a few extra food.
Later policies in the Tradition tree will also grant food and growth bonuses, not to mention free aqueducts, so complete this tree sooner rather than later. The Aristocracy policy will also give you a bonus towards wonder-production, which you can use towards the Hanging Gardens or Temple of Artemis world wonder. The Artemis wonder increases total food instead of excess food, which means it is beneficial even if your cities aren't generating much excess food.
If you start with an good variety of luxuries and food resources, then the Iroquois are actually very well-suited to a Liberty start as well. Rapid expansion allows you to claim more forested cities, and the Great Warpath will ensure that Meritocracy's bonus happiness should be easy to achieve. The faster improvement rate from Citizenship will let you get lumbermills and camps built more quickly, and Republic will give you an early boost to city productivity.
Try to expand such that your cities are connected by unbroken lines of forest and/or jungle. Once you research The Wheel, and your borders expand to fill in the space between the cities, they'll automatically establish city connections. This spares you from having to spend time building roads with your workers, and allows them to focus on improving resources. It also benefits the economy by sparing you the maintenance costs associated with roads! If your cities are very spread out, or if the forests or jungles are sparse, then you may have to build some roads in the gaps in order to complete your city connection links. If necessary, use gold to purchase forested or jungle tiles that will help create unbroken lines between your cities.
Despite Great Warpath, you may still have to build roads outside your borders to connect spread out cities.
On higher difficulties, the A.I. will start the game with bonus technologies and a free worker (allowing them to more quickly improve terrain). If large expanses of forest lie between you and an A.I. opponent, you'll be more likely to be able to establish a trade route with their cities. You can use the boost in caravan range to leech some research and extra gold out of them and help you get off to a better start technologically.
Avoid chopping forest if possible, but if you absolutely need to chop to make room for farms along rivers, then try to leave an unbroken line of forest between your cities so that you can benefit from maintenance-free city connections and quicker movement between your cities. Assigning a couple caravans to transport food between your cities can also help keep them growing without having to chop forest to build farms. You can also feel free to sell all of your iron (if you have any) to other (preferably friendly) civs in order to keep an extra buffer of gold while you use your trade routes for food shipments. You won't be needing iron at all until the late medieval era anyway.
After you have your local luxury-improvement techs researched, move on to Construction, Guilds, and Metal Casting fairly quickly so that you can fully improve your forests. Assuming that you are able to generate enough food to keep your cities growing, start building carpets of lumbermills and trade posts on your forests. With Longhouses in your cities, forest tiles will be very productive, and you trade posts will generate some gold as well.
Workers can quickly cross rivers and forest
to get to terrain that needs improving.
If you were able to settle in heavily forested areas, then you'll find that movement within your territory will be very rapid. In addition to acting like roads, forests and jungles also act like bridges (even before researching engineering), allowing you to cross rivers from the start of the game! This can be very helpful for moving your troops around to defend against barbarians, aggressive neighbors (like Montezuma or Shaka). Your workers will also be highly mobile, as they'll be able to move through forests and across rivers to get a head start on improving terrain. You should be able to get your local resources improved very rapidly.
Even though your Mohawk Warrior doesn't require iron, you still have to research Iron Working in order to unlock it, which means that you'll have to go through Bronze Working and reveal iron. If you have any iron in your territory, go ahead and improve it and then sell the iron to friendly civs for some extra gold. Assuming that you have plenty of forest or jungle in your territory, the Mohawks will be excellent defensive units. Wait for invading units to enter your forest or jungle tiles. Then use the ability to travel along forests and jungles to rapidly mobilize against invading opponents, surround their units to gain flanking bonuses, and then ambush them on the forests to use the combat bonus.
You can also use your mohawk offensively. They aren't any stronger than the regular swordsman, but you should be able to build a lot of them in order to overwhelm opponents, and you don't have to worry about penalties if you lose access to iron. The combat bonus on forests or jungles applies in neutral and enemy territory, so you can effectively invade other civs who are reliant on their own forests or jungles to provide protection. Target civs that live in forested areas and which have access to iron. Civs like the Celts, and Brazil won't be able to hide in a shield of forests or jungles, as your units will be able to break their defenses. The Aztecs, on the other hand, will be tough to crack, since their units also receive bonuses in forest and jungle.
Civs that rely on forest and jungle for protection will be vulnerable to Iroquois Mohawks.
If you capture any enemy cities, be sure to bring some workers along to delete any roads that the former owner may have built on forests.
May the spirits of the ancestors guide you
The Iroquois were an example of a vanilla civ that really benefited from Gods & Kings' religion mechanic. Prioritizing a pantheon can really help offset some of the Iroquois weaknesses. Having lots of forest in your territory can severely impact your food production, especially if you don't want to cut down the forest to make room for farms (thus reducing the effectiveness of your Longhouse). Forests generally generate a lot of camp resources such as deer, furs, and truffles. Adopting the Goddess of the Hunt pantheon will ensure that those camps will at least be able to support the citizen working them and keep the city growing. Fertility Rites can be a good backup option if someone else beats you to Goddess of the Hunt. You can follow these up with Feed the World or Swords Into Plowshares when you found your religion in order to further boost your food and growth. If your food output is high and you plan to expand rapidly (especially with the Liberty tree), then Messenger of the Gods can be a powerful pantheon. Most (or all) of your cities should hopefully be connected by the Great Warpath, so you'll get a very early research bonus from this pantheon.
If you get a jungle start or a lot of food resources, then you should be OK when it comes to food, but may suffer from limited production. The Longhouse won't help you here, so founding a religion in order to get Religious Community can help increase your production a little bit. In the meantime, pantheon beliefs such as Sacred Path and Oral Tradition can give you a hefty boost to culture in the jungles or the the plantation resources that usually spawn in them. Sun God can also be a good pantheon if you get a lot of citrus or bananas.
Goddess of the Hunt can offset the lack of food in forest tiles and enable Iroquois to work those forests.
You might want to open Piety and the Organized Religion policies early in order to beat others to your first prophet in order to guarantee that you get the pantheon that most suits your needs. The good thing is that a lot of the religion follower beliefs that benefit Iroquois are not the ones that typically get chosen first, so you don't have to be under as much pressure to rush to your second prophet to upgrade your pantheon to a religion. But generally, you'll still want these bonuses sooner rather than later, and the religious buildings are always good to have (if you can get them).
Forests and jungles will also increase the range of your caravans (even in neutral territory). This can allow you to set up trade routes with cities further away in order to apply pressure and spread your religion further. Religious Texts or Religious Unity enhancer beliefs will speed up the spread of your religion, which can begin accumulating strong benefits for you. Alternatively, you can adopt Itinerant Preachers enhancer belief to spread religion to cities further away, and then use the increased range of your caravans to leapfrog your religious pressure beyond even that range!
If you see other civs nearby that are spreading their own religion, then try to protect your cities with some inquisitors to ensure that you don't lose access to the pantheon and religious beliefs that are supporting your growing cities. You'll also want to avoid granting open borders to such civs in order to reduce the effectiveness of any misisonaries that they do send to your cities.
Longhouses and Hydro Plants make lumbermills very productive.
Gunpowder, railroads, and beyond
The second half of the game doesn't require much active effort by the player, as most of Iroquois' uniques are either already in place or have become obsolete. You should already have your forests improved with lumbermills and have longhouses built in any forested cities that would benefit from them. So now it really just comes down to coasting along till the end of the game.
Mohawk Warriors don't obsolete until Gunpowder, so there is a window of time in which you'll be able to build either Mohawks or longswords. Be sure not to renew deals in which you trade away iron during the medieval era so you can keep a buffer supply to upgrade to Longswords. Or renegotiate so you keep some iron in your supply. Build Mohawks to get their forest combat bonus, then pay to upgrade them to Longswords. When you research gunpowder, you can go back to selling your iron, unless you need it for Frigates.
Infantry upgraded from Mohawk Warriors can be used to defeat foes that are fortified in forests and jungles.
If you're playing for a Domination Victory, then try to keep some friends and allies so that you can benefit from the movement bonuses when moving along any forests or jungles in their territory. If the Aztecs, Celts, or Brazil are still in the game, then they can be good allies. They usually keep plenty of forest and jungle in their territory due to their uniques, so you won't have to worry about your own units being bottlenecked on their roads when passing through their territory. Ambush your opponents in forests and jungles whenever possible, since you should still have plenty of modern units that are upgraded from Mohawks and which still receive the +33% combat bonus in forest and jungle. Just stay out of a land war with the Aztecs, since their units will be at least as strong as yours in jungles and forests.
When you get into the modern era and research Railroad, your forests will automatically provide the railroad production bonus to connected cities! The movement bonus within the forests does not increase, so you might still want to build rails in order to facilitate even faster unit movement. But that's really only necessary if your empire is very spread out. If you still have a large carpet of forest or jungle in your territory, then the rail network will mean that travel to anywhere within your borders will be virtually instantaneous. You'll also need to explicitly build rail to cities that are not connected by forest.
Great Warpath provides the rail production bonus to forest-connected cities for free,
but you might still want to build rail in order to get faster movement through your territory.
As you progress through the later eras, your production bonuses in forests will help you to build victory-specific buildings, such as Broadcast Towers and Hotels for Culture Victory, or the Public Schools and Spaceship Parts for a Science Victory. You'll also have more production late-game to spend on projects proposed by the World Congress. You'll have an edge over most other civilizations to get the top award in World Games, World's Fair, or the International Space Station.
Be advised that using archaeologists to dig for artifacts in forests or jungle will remove the forest or jungle, regardless of whether you chose to take the relic or build the landmark. This late in the game, the forests shouldn't be as important as they were earlier. Railroads, airlifts, planes, and paratroopers should all allow you to defend your territory fairly effectively. So losing a few forests here and there shouldn't be a problem. If a landmark spawns on a forest or jungle that is integral to a city connection, then be sure to send a worker along to build a road. If you already have railroads in place, then this probably won't be necessary.
Archaeological digs remove underlying forest or jungle.
I tend to go with the Freedom ideology when I play Iroquois. Military is usually my last-resort victory plan for them, so Freedom has tenets that focus on the remaining victories. Your ideological choice is mostly dependent on your own playstyle and victory plans. Tenets that produce food (such as Freedom's Civil Society or Order's Party Leadership) can help keep your cities growing in the late game, despite the proliferation of 1-food forest tiles. If you had enough forests to make Longhouses worthwhile in all of your cities, then Order's workshop and factory-buffing tenets can also be very beneficial.
Dealing with non-optimal maps
Iroquois is one of the most map-dependent civilizations in the game, and the strategies outlined here can be completely derailed if you get a poor map or start location. You'll rarely find yourself starting the game in a large carpet of forest. Typically, you'll find yourself in a spotty forest or jungle start. If you can see a large, forested area nearby, then you should seriously consider moving your settler closer to the forest. From there, you'll want to try to expand your first couple of cities into the nearby forest, putting priority on camp-based resources. If you have spotty forests, then try to use as much of the forest to augment your road network as possible, and buy forested tiles that will allow you to connect your cities.
If you're stuck in a jungle, you'll likely have to cut a lot of the jungle down in order to improve the underlying resources. The Longhouse doesn't work in jungles, so cutting them down isn't as much of a loss as chopping forest. Try to avoid chopping jungles that don't have resources so that you can benefit from the Great Warpath ability and combat modifiers. Build trade posts over these tiles and put priority on researching Education so that you can build Universities and start getting research from your jungles.
Build roads connecting forests and jungles in order to establish city connections.
Worst-case scenario: you have no jungle or forest. In this case, the Longhouse might not even be worth building, especially if you have limited gold. If you built any engineer-producing wonders like the Temple of Artemis, Pyramids, or Great Mosque, then you can maybe put a Longhouse in that city in order to fill the specialist slot and generate more engineers. Otherwise, its really only useful as a prereq for the Iron Works and Factories, and you might want to delete worthless Longhouses after building a factory in that city. Use internal trade routes to supplement your limited production in your key unit-producing and wonder-building cities, and use an additional trade route to help develop any newly-founded cities.
If you have good enough resource diversity with other civs within range, then you can consider neglecting production in favor of highly-profitable trade routes. Use gold to buy buildings and units instead of hammers. Your caravans can use forests and jungles in neutral territory to increase their range, so you can use this feature to hopefully get access to some better trade options. Just make sure that you send some escort units with them through neutral territory so that they don't get plundered by barbarians in the fog of war. If you get a coastal start, you can instead orient your economy entirely around cargo ships.
At the very least, you still get a unique swordsman that doesn't require iron, and they'll still get a combat bonus in forests and jungles in neutral or enemy terrain. Build a bunch of Mohawks if you need to protect yourself from mid-game invasion, and sell any iron you have to keep your economy strong and pay for their upkeep. You'll probably also want to lean more towards the trade bonuses of the Freedom ideology, since you may not have enough Longhouses in your cities to benefit from Order's workshop and factory-buffing tenets.
Detouring Hiawatha's Great Warpath - Countering Iroquois
I have found the Hiawatha A.I. to be one of the most dangerous and competitive A.I.s in the game (and I'm certainly not alone in that assessment). He seems to have the perfect combination of expansiveness, aggression, and diplobalance, and he is always a threat in my games. He builds new cities rapidly and almost always has a strong defensive army (possibly due to not needing iron).
Hiawatha frequently builds defensive wonders like the Great Wall, and Himeji Castle. Having to invade an empire surrounded by the Great Wall, and full of a carpet of forest is hard enough. Throw in the mobility and combat bonuses of the Mohawk (which alleviates the A.I. general tactical incompetence), and it becomes nigh impossible until Dynamite. In many cases, Hiawatha is also strong enough to steamroll over other A.I.s, and I routinely see him repel invasion from the likes of Napoleon, Alexander, Montezuma, Nobunaga, Augustus, and even Shaka, only to turn around and capture their capitals!
Despite being so strong, Hiawatha is rarely openly hostile. His aggression and deception balance is one of the lowest in the game, and his loyalty score is one of the highest. If you make friends with him early, he'll likely remain your friend for most of the game as long as you don't oppose him in the world congress or adopt a competing ideology (he seems to prefer Order whenever I play against him). Hiawatha's warmonger dislike is also on the higher end, so he can turn on you rather suddenly if you start capturing capitals or city states. His expansive empire usually results in a strong economy and scientific output, making him a frequent leader in the technology race and a danger for winning a Space Race Victory.
Iroquois lands can be virtually impenetrable if Hiawatha builds the Great Wall.
Hiawatha is also deeply religious, and will almost certainly found a religion and/or pantheon. Expect him to take pantheon beliefs such as Goddess of the Hunt, Oral Tradition, or Goddess of Protection. If you want any of those beliefs for yourself, then you'll need to put extra priority on early faith.
A player-controlled Iroquois is less likely to be as dangerous as the A.I. one, since the player lacks the handicaps (at the higher difficulties) that really help push Hiawatha over the edge. Whether playing against a human or A.I.-controlled Iroquois, they can still be a good ally or trade partner. Iroquois units are good defenders - especially in forests and jungles, and the Iroquois will likely be willing to sell any iron that they possess.
If the Iroquois have the advantage of a large forested or jungle area, then they can be very difficult to defeat in battle. You'll either have to rush them before they can build Mohawks, or wait until you have artillery and planes to attack over the forests. Even your longswords will be vulnerable to the forest/jungle combat bonus and defensive mobility of the Mohawk. Limiting Iroquois' access to iron won't help, since their Mohawks don't require it.
If you're having trouble with the Iroquois, then consider bringing some workers along with your army to just chop down the forests or jungles in Iroquois territory. Focus on any forests that are necessary links in the Iroquois city connection network so that you can weaken their economy. You can also aim to chop forests and jungles on hills so that you can get the defensive bonus on the hill without the Iroquois getting any of their forest/jungle bonuses from that tile when they attack you. You cannot chop forests in other players' territory by using open borders, so if you want to chop Iroquois forest, you either have to do it before they settle the territory, or do it while in a state of war.
Using workers to chop down Iroquois forests is an effective way to permanently neutralize their uniques.
Discuss this strategy on Civfanatics:
or on the official 2K Civilization V forums:
or on Reddit :
Listen to the discussion on PolyCast, Episode 247, 05m56s (January 30th, 2016):