NONE There were no atomic bombs used in World War 1. It wasn't invented until the end of the Second World War. Hiroshima and Nagasaki, in Japan, were bombed at the end of World War 2. World War I ended with the Treaty of Versailles in 1919.
The League of Nations was formed after World War 1 and fell apart as a reslt of World War 2. The United Nations formed toward the end of World War 2, initially as an organization of nations opposed to the Axis Powers.