In August 1914, two European coalitions stumbled into war. On one side were the Central Powers: the German and Austro-Hungarian Empires. Quickly they were joined by non-European Turkey and later by a third European (Balkan) nation, Bulgaria.Facing them was the Triple Entente, comprised of Russia, France and Great Britain and her empire, plus Belgium, Luxembourg, Serbia and Montenegro. Through the course of the war a number of other European powers found it in their interests to enlist with the Allies, including Italy, Romania, Portugal and Greece.
From the beginning, France and Great Britain utilized troops from their empires first to defend their colonial possessions around the world from Africa through Asia to the Pacific Ocean and, second, to provide manpower in the main combat arena on the Western Front in France as well as in the Middle East. Even at the start, participation in the Great War was trans-European.--World War I Historical Association
Soon, the Middle East, Asia, and the United States were also involved.
This year marks the 99th anniversary of the declaration of the first World War.