Russia suffered the most casualties during World War I, with an estimated 1.7 million soldiers killed and 4.9 million wounded.

The Treaty of Versailles was the main peace treaty that ended World War I. It was signed on June 28, 1919, between the Allied Powers and Germany.

The United Kingdom gained the most territory as a result of World War I, acquiring control over former German colonies in Africa, the Middle East, and the Pacific.

The League of Nations was an international organization that was created after World War I to promote peace and cooperation. It was founded on January 10, 1920, and was headquartered in Geneva, Switzerland.

The United States was the first country to withdraw from the League of Nations. It did so in 1920, after the U.S. Senate refused to ratify the Treaty of Versailles.

The Great Depression was an economic crisis that occurred in the 1930s, which was partly caused by the aftermath of World War I. It began in the United States in 1929 and spread to other countries around the world.

Germany was the first country to invade Poland during World War II. It did so on September 1, 1939, which marked the beginning of the war.

The Axis Powers was a military alliance between Germany, Italy, and Japan during World War II. It was formed in 1940 and lasted until the end of the war in 1945.

The United States was the first country to drop an atomic bomb during World War II. It dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki in August 1945, which led to the surrender of Japan and the end of the war.

The United Nations is an international organization that was created after World War II to promote peace and cooperation. It was founded on October 24, 1945, and is headquartered in New York City.

The United States was the first country to join the United Nations. It did so on October 24, 1945, the day the organization was founded.

The North Atlantic Treaty Organization (NATO) was a military alliance between the United States, Canada, and Western European countries during the Cold War. It was founded on April 4, 1949, and is headquartered in Brussels, Belgium.

The Soviet Union was the first country to launch a satellite into space. It launched Sputnik 1 on October 4, 1957, which marked the beginning of the Space Age.

Neil Armstrong was the first human to walk on the moon. He did so on July 20, 1969, as part of the Apollo 11 mission.

The World Trade Organization (WTO) is an international organization that was created in 1995 to promote global trade. It is headquartered in Geneva, Switzerland.