WW1 destroyed the Europeans' romantic notions as thoroughly as our own Civil War did ours. The Christmas truce had been traditional in European warfare until then - along with all the other trappings of chivalric war that died in mud, blood, and clouds of poison gas in 1914-1918.
I am of the opinion that the reason we see so much pacifism in Europe today is because of WWI, WWII. This too shall pass.