WWI, The War to End All Wars.
It was supposed to be short; the soldiers were supposed to be home for Christmas. But it turned out to be a long, arduous stalemate, thanks to the fiery birth of modern warfare; machine guns, airplanes, day after day spent digging miles of trench. No more valiant marches to the front lines, no more decorated uniforms in bold colours, no more bayonettes. Traditional chivalry was misplaced somewhere in the chaos of No Man’s Land. WWI had changed the face of war forever, and they did not expect it.
EDIT: Today is November 11, the day Armistice was declared. There is in fact a poppy in Hungary’s hair =)
(I can’t remember if I put this on tumblr already, but I’m in such a history mood right now and I have nothing else to offer…)
top to bottom): Austria-Hungary, Russia, France, Germany (Prussia included), Great Britain, United States of America, Italy (South Italy included). Though this is not everyone who participated!