The Treaty of Versailles was the treaty that ended World War I. That war lasted from 1914 to 1918. The treaty was written up after the war ended and was signed in 1919.
The Treaty of Versailles was essentially imposed on Germany by the victorious allies. The main countries that were involved in writing the treaty were the United States, France, the United Kingdom, and Italy. Because they had defeated Germany in the war, they did not feel that they had to negotiate with Germany. Instead, they simply presented the treaty to Germany and told them to sign it or risk the resumption of the war.
The Treaty of Versailles is widely felt to have been unfair to Germany. It was certainly very harsh. It took much of Germany’s territory, both in Europe and in the rest of the world, away from Germany. It prohibited Germany from having real armed forces of any size. It required Germany to admit that the war was its fault and it forced Germany to pay reparations for the war to the allies. Because of this, the treaty caused a great deal of anger among Germans and it is seen as a major cause of World War II.