Russia suffered the most casualties in World War I, with an estimated 1.7 million soldiers killed.

The Treaty of Versailles was the peace treaty that ended World War I. It was signed on June 28, 1919, in the Hall of Mirrors at the Palace of Versailles in France.

Germany was forced to pay reparations after World War I as part of the Treaty of Versailles.

The League of Nations was the international organization that was created after World War I to promote peace and cooperation.

The Great Depression was the global economic crisis that occurred in the 1930s.

Poland was the first country to be invaded by Nazi Germany in World War II.

Little Boy was the atomic bomb that was dropped on Hiroshima, Japan, in 1945.

Fat Man was the atomic bomb that was dropped on Nagasaki, Japan, in 1945.

The United States was the first country to develop a nuclear weapon.

The Truman Doctrine was the Cold War policy of containment.

The Soviet Union was the first country to launch a satellite into space.

Neil Armstrong was the first human to walk on the moon.

The United States was the first country to develop a personal computer.

The Internet was the global computer network that was developed in the 1960s.

The United States was the first country to develop a smartphone.