World War I, also known as the Great War, engaged all the great powers of Europe, and their worldwide colonial empires, including South Africa, German East Africa, French West Africa, Morocco, Algeria, Egypt, India, Vietnam, Australia, New Zealand, the West Indies, and Canada. The United States, Japan, and China also entered the conflict. More than 70 million military personnel were mobilized by all nations. The modern industrial capacity of the principal combatant countries fueled one of history’s most destructive wars.
The Allies and the Central Powers
A complex set of long-standing pre-war alliances between the major powers of Europe brought country after country into the war after the heir to throne of the Austro-Hungarian Empire was assassinated by a Serbian nationalist in June 1914, triggering an invasion of Serbia by Austria-Hungary. Within weeks the world was at war. Great Britain, France, and Russia—the Allies—joined forces against Austria-Hungary and Germany—the Central Powers. The United States, Italy, and Japan joined the Allies. The Ottoman Empire and Bulgaria entered the war on the side of the Central Powers.
America Enters the War
President Woodrow Wilson pledged to keep America out of the war. But his stance of non-intervention was severely tested on May 7, 1915, when a German submarine sank the British ocean liner RMS Lusitania. Of the 139 Americans on board, 128 perished. Germany had declared the seas around the United Kingdom a war zone, and felt justified in attacking ships believed to be bringing supplies to support the Allied war effort. The Lusitania was indeed carrying munitions, although the British denied this at the time.
Wilson demanded an end to attacks on neutral passenger ships, and the Germans complied for a time, only targeting ships that were clearly British. But in January 1917, Germany resumed unrestricted submarine warfare in the Atlantic shipping lanes. This action, and the American response of outrage to the discovery of the Zimmermann Telegram, a secret communication from Germany to Mexico proposing a military alliance, prompted President Wilson to reverse his 1916 re-election campaign promise to keep the country out of the conflict.
The United States entered the war on April 6, 1917, with troops arriving in Europe in early 1918. The infusion of fresh American forces helped carry the war-weary Allies to victory.
The End of Hostilities
After four grueling years of stagnant trench warfare, characterized by many technological innovations that contributed to the brutal nature of the battlefield, an armistice ended hostilities on November 11, 1918. The peace settlement negotiated in Versailles, France, imposed harsh terms on the Central Powers, dismantling their empires into many newly created nations, and requiring them to pay crippling reparations to the Allies. German humiliation and bitterness over the terms of the Treaty of Versailles in part contributed to the rise of Nazism and World War II twenty years later.
World War I dramatically refashioned the map of Europe and the Middle East, laying the foundation for later conflicts, including World War II, the Cold War, and recent clashes in the Middle East. The First World War spawned numerous revolutions, the most significant in Russia in 1917, leading to the creation of the Soviet Union.