1910s: After World War I ends, forty-two countries, not including the United States, join the League of Nations, an organization officially established in 1920 with the intent to help maintain peace throughout the world.

Today: As of 2001, 189 countries around the world are member states of the United Nations. The UN was formed in 1945, ultimately replacing the League of Nations, with the dual mission of maintaining international peace and security and deterring aggressors.

1910s: By the middle of the decade, countries around the world are involved in World War I.

Today: Numerous regional conflicts are taking place in many locations around the world, such as the ongoing conflicts between Israelis and Palestinians in the Middle East or between Catholics and Protestants in Northern Ireland. The United Nations and countries around the world, particularly the United States, have been involved over the years in peace-brokering attempts.

1910s...