The document summarizes the key causes and events of World War 1. Nationalism, militarism, and collapsing empires increased tensions between European powers. Specifically, rivalry between Austria-Hungary and Serbia over Balkan territories was a major trigger. When the Black Hand assassinated Archduke Franz Ferdinand, Austria-Hungary used it as a pretext to invade Serbia, drawing in allies through a system of entangling alliances and launching the world into the first modern industrial war.