@artemis In Canada this still happens, despite having > 2 major parties. The us/them line just gets placed differently for differing "us" - so the Parti Quebecois has a "them" of all Anglo parties, the Conservatives say everyone else is a crazy leftist, the NDP don't play this game as much but aren't a major player these days, the (neo-)Liberals portray the Conservatives as the only "real" opposition and lock discourse into the narrow band between neolib and conservative positions, and describe the other parties as insignificant because of both size and policy. The Greens claim no other party is environmentally or socially responsible.

All of these except maybe the waning NDP definitely use "beat the other [real] side" positioning to lock in supporters who are supporting their "favourite team."