World War I was a large-scale military conflict involving European nations, United States and other nations across the world. The war lasted from August 4, 1914 to November 11, 1918. More than 15 million people were killed and 20 million people were wounded, making it one of the most devastating conflicts ever. The war ended with the defeat of the German Empire, the Austro-Hungarian Empire, Ottoman Empire, and the Russian Empire. The League of Nations, an inter-governmental organization, was formed in the hope of preventing another such conflict, but it failed to prevent the World War II, a larger and deadlier global war that started in 1939.