Peace treaty signed 28 June 1919
The act which is considered to have triggered the succession of events which led to war was the 28 June 1914 assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian throne, by Gavrilo Princip, a Bosnian Serb citizen of Austria-Hungary and member of the Young Bosnia. The retaliation by Austria-Hungary against the Kingdom of Serbia activated a series of alliances that set off a chain reaction of war declarations. Within a month, much of Europe was in a state of open warfare.
The war was propagated by two major alliances. The Entente Powers initially consisted of France, the United Kingdom, Russia, and their associated empires and dependencies. Numerous other states joined these allies, most notably Italy in April 1915, and the United States in April 1917. The Central Powers, so named because of their central location on the European continent, initially consisted of Germany and Austria-Hungary and their associated empires. The Ottoman Empire joined the Central Powers in October 1914, followed a year later by Bulgaria. By the conclusion of the war, only The Netherlands, Switzerland, Spain and the Scandinavian nations remained officially neutral among the European countries, though many of those provided financial and material support to one side or the other.
The fighting of the war mostly took place along several fronts that broadly encircled the European continent. The Western Front was marked by a system of trenches, breastworks, and fortifications separated by an area known as no man's land.[5] These fortifications stretched 475&_160;miles (more than 600 kilometres)[5] and precipitated a style of fighting known as trench warfare. On the Eastern Front, the vastness of the eastern plains and the limited railroad network prevented the stalemate of the Western Front, though the scale of the conflict was just as large. There was heavy fighting on the Balkan Front, the Middle Eastern Front and the Italian Front; there were also hostilities at sea and in the air.
