Worksheet Answers Three main reasons of tensions between European countries in the early 1900s…. Nationalism Militarism Entangled alliance Nationalism -populations devoted to interests in their own nations, national pride. Alliance- countries tied to one another in a series of binding military treaties Triple Alliance (became the Central Powers) Austro-Hungarian Empire Germany Italy * *At the beginning of the war, Italy did not honor its alliance with Germany/Austro-Hungarian Empire and switched to fight with Great Britain, France, and Russia The United States observed the policy of neutrality or noninvolvement.