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most fun game we played was with 6. we played again with 8 and there were just too many players on the board for it to be enjoyable. no one was really able to get a continent bonus, or get enough territories to get more than 3 troops a turn. The people that could get more just camped and waited. My groups' opinion is that with 6 players is the most fun way to play this game.
that said, I won both of the games. My strat was simple: collect a resource card every turn, turn in cards for 30 troops and make a surprise attack on multiple bases in the same turn.