The outbreak of World War I deeply eroded the network of international friendships and connections built up in the preceding years by historians in Germany, France, Great Britain, and the United States. Both sides argued that the war was waged between two different cultures; the French and British attacked German aggression and militarism and its historical roots, while the Germans stressed their greater commitment to social responsibility and the superiority of German 'Kultur.' American historians also joined the official war effort once the United States entered the war in 1917. Though a few scholars continued to support an international community, the war was used as an excuse both in Europe and the United States to dismiss university professors whose views did not conform to the pro-war position of the majority. The hard-line position taken by many German historians persisted after the end of the war and led to their increasing isolation on the international level.