They didn't take any part against Voldy's first run at power, either. For that matter, Dumbledore let Grindelwald run roughshod on the Continent for several years before finally raising a hand against him. It seems to me that there was precedent for the Continent to do nothing, especially when Voldemort himself, even after the fall of the Ministry, still controlled things from behind the scenes.
There were wizards in Britain who didn't want to take action against Voldemort, and they were directly threatened; for those on the Continent, what was happening in Britain must have seemed quite far away and none of their business.
rendering the whole premise of the Tri-Wizard Tournament in Goblet of Fire pointless.
It was the *hope* of the Tri-Wizard Tournament to build understanding and better relations among the different parts of the magical world... there was no real indication that it worked, though. After all, what real good do the Olympic Games do in that regard?
They were a great showcase for Nazi Germany in 1936...