Canadian politics is greatly influenced by its "third parties," like the NDP or the Bloc Quebecois.  Third party options have been present to Canadians for the majority of our history. No Canadian today can remember a time in Canadian politics when third parties did not have some sort of influence, but for the first half century of Canadian political history, Canada was essentially a two-party system.  All of that changed in 1919 after the First World War.