One of the weaknesses of Star Trek: Ascendancy (in my opinion) is the simplicity and irrelevance of the game's "minor races". They just sit there waiting to be invaded or hegemonized. They don't even have ships in orbit to defend themselves from attack (or provide the Klingons with an opportunity for some easy culture). I had hoped that there'd be an expansion pack that would give at least the warp-capable civilizations a little bit of agency. Sadly, that hasn't happened yet, but Gale Force 9 has released an expansion that does add an NPC faction: the Borg.
How do Borg allocate damage between multiple fleets?
The Borg are not a player faction (like the excellent Cardassians or Ferengi expansions). The Borg are a non-player "A.I." entity that use a deck of cards to define their behavior. They act in opposition to every player in the game, and are intended to add some extra player-versus-board challenge. The Borg expansion also adds rules for solo and 2-player games, though I'm not terribly happy with how either of those variants plays.
The big problem is that the rules for the Borg cause a lot of confusion. The non-player element of the Borg creates a lot of strange edge cases that the rulesmakers just didn't seem to think through very thoroughly. Some rules leave the Borg's actions somewhat ambiguous, and there are no rules for determining how to resolve such situations. For example, if a Bog cube is battling multiple fleets belonging to the same player, how does it determine which fleet takes damage? We generally house-rule that the Borg attack the largest fleet first, and that the player who activated the cube decides any ties.
The enemy of all my enemies
The bigger problem, however, is that the Borg movement rules lead to considerable balance issues once the Borg are connected to one player, because that poor player now faces the brunt of the entire Borg Collective. Once the Borg have a path to any one player's systems or homeworld, the Borg will exclusively funnel all of their ships down that one path, since it's the only "connected" route available. The only way this will change is for the targeted player to go out of his or her way to try to create another, shorter path to one of the other players (essentially painting a huge target on that player's head). Or I guess one of the other players could accidentally create a shorter path while they're exploring, if they're dumb or not paying particularly close attention. In any case, the problem is that once the Borg become connected to any one player, the Borg stop exploring and looking for the other players, which randomly puts the single player in a disadvantaged defensive position while the other two players are free to build up without much threat of being targeted by the Borg.
Having the Borg in play gives further reason for players to cooperate.
The game tries to offset this by making it so that the Borg become more powerful if they assimilate any worlds (including warp-capable civilizations), or if they assimilate any one player. If your homeworld is assimilated by the Borg, you even get to take over as a Borg player, taking a whole extra Borg turn in which you get to influence how they behave. This is a fun and thematic way of allowing an eliminated player to continue to participate in the game and seek some degree of "revenge" against the other player.
The idea here is that the players shouldn't let the Borg concentrate on wiping out a single player, and we should all partially co-operate in order to keep the Borg in check. There is no actual co-operative victory, so you're only co-operating with each other to the ends of stalling the Borg long enough for you to achieve a victory, at the expense of the other players. There is no "defeating" the Borg.
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