History Essay The main causes of war are militarism, alliances, imperialism, and nationalism. Militarism is a strong military spirit or a belief that you have the best miliary force and can defeat an opponent. Alliance is the merging of efforts or interest by two or more groups. Imperialism is the policy of extending the rules or authority of a nation over foreign countries or by acquiring colonies. Nationalism is the devotion of interest to one's own nation. Militarism was found as one cause of World War I. Austria-Hungary had attacked Serbia. Russia entered the war to help Serbia. Germany declared war on Russia, believing that Russia's military was otherwise occupied. Germany felt they had the military strength to come out the victor. Because of their alliances, the United States joined the war to support their allies, including France, Russia, Italy, Japan, Britain, and Belgium. The Slavic people in Bosnia and Herzegovina no longer wanted to be part of Austria-Hungary but instead they wanted to be part of Serbia. By their show of nationalism or patriotism