World War I started in 1914 and ended in 1918. At first, people called it the Great War and thought it would end all wars. It was the biggest war the world had seen up to that time. Most of the fighting took place in Europe and the Middle East. Over 8 million soldiers and sailors died, and more than 20 million were hurt in the fighting.
The war started when a prince was shot in a city called Sarajevo. Sarajevo was in a place called Bosnia, which was part of a big empire called Austria-Hungary. Austria-Hungary and its neighbor Serbia didn't get along. Some Serbians wanted their country to be free from Austria-Hungary's rule. On June 28, 1914, a Serbian shot and killed Archduke Franz Ferdinand, a prince from Austria-Hungary. Austria-Hungary said Serbia planned it.
On July 28, 1914, Austria-Hungary declared war on Serbia. Both countries asked their allies for help. Austria-Hungary's main allies were Germany and the Ottoman Empire. They were called the Central Powers. Serbia's allies were Russia, France, and the United Kingdom (Great Britain). They were called the Allied Powers.
At first, the United States remained neutral, which meant it did not take sides or fight in the war. President Woodrow Wilson did not want the United States to get involved. In 1917, the United States joined the Allied Powers. Germany had been attacking U.S. ships, and the United States also learned that Germany had promised part of the U.S. to Mexico if Mexico helped Germany in the war. The United States declared war on Germany on April 6, 1917. That same year, a major change called the Russian Revolution took place in Russia. Russia's new government made peace with the Central Powers and left the war in early 1918.
During the war, both sides tried new ways to fight. Many soldiers fought from long, dug-out ditches called trenches, which stretched for miles across the battlefields. Both sides also used submarines to attack ships at sea. They also used poison gas, tanks, and airplanes for the first time. Germany bombed the United Kingdom with zeppelins, which are big floating aircraft. Later, both sides built airplanes for fighting and bombing. The war changed how people fought wars forever.
By 1918, the Central Powers were running low on soldiers and supplies. One by one, Germany's allies stopped fighting and surrendered. On November 11, 1918, Germany agreed to stop fighting and signed an armistice, ending the war. The Allied Powers had won, but the war had cost millions of lives on both sides.
