The assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian Empire,, by a Serbian nationalist set off a chain of events that activated a complex set of alliances. Austria threatened tiny Serbia; the Russian Empire backed Serbia; Germany supported Austria; and France supported Russia. Germany’s decision to violate Belgian neutrality brought both Belgium and Britain into the war. After a few months of marching in the beginning of World War I, the Allied countries (Russia, France, Belgium and Britain) and the Central Powers (Germany and Austria-Hungary) found themselves facing each other across massive lines of fortifications that stretched across Europe. Three years of bloody attacks produced terrifying casualties but failed to end the stalemate. Aware that Britain was dependent on maritime trade for survival, Germany risked American involvement by commencing unrestricted submarine warfare in 1917. However, the strategy not only failed to strangle Britain, but also forced the United States to abandon its neutral stance and enter the war. The Russian Empire collapsed in the spring of 1917, and the formation of the Soviet Union following the October Revolution meant that Germany no longer had to fight on two fronts. Hoping to achieve victory before the United States could ship over enough soldiers to tip the balance on the side of the Allies, Germany launched a final series of offensives in the spring of 1918. Although the German offensives almost broke through, the Allies counter-attacked and achieved total victory by November. By the end of the war, the German, Austro-Hungarian, Russian and Ottoman Empires had ceased to exist.