1) By the early 1900s, several factors had pushed Europe towards war, including nationalism, imperialism, militarism, and a system of complex alliances between countries.
2) Germany launched a surprise attack on France by invading Belgium, drawing the United Kingdom into the war on the side of the Triple Entente alliance against the Triple Alliance.
3) In August 1914, World War 1 began in earnest with Germany and Austria-Hungary fighting against Russia, France, Britain and their allies.