Some blamed Russia, the first big country to mobilize. Some blamed Germany for the inflexibility of the Schlieffen Plan. Leninists claimed the war grew out of imperialism and was fueled by capitalist rivalries. And others claimed it was a war between Germany's radical modernism and Britain's traditional conservatism. But if I had to assign blame, I'd go with the alliance system and the cultural belief that war was, in general, good for nations. War helped define who was them and who was us, and doing that strengthened the idea of us. And in World War I, war was perceived to be necessary and often even glorious.