The first assembly of the League of Nations is held in Geneva, Switzerland.

The League of Nations started out with a lot of hope after World War I, meant to keep the peace by giving countries a place to sort out conflicts before they turned into something worse. It was basically the world’s first big attempt at a global peacekeeping organization, built into the Treaty of Versailles in 1919. The idea was solid for its time: collective security, open diplomacy, and cooperation instead of constant rivalry. But even from the beginning, the League was missing key players and didn’t have the authority or muscle to enforce much.

One of its biggest problems was that the United States—ironically the country whose president, Woodrow Wilson, pushed hardest for the League—never actually joined. Without the U.S., the organization had less political and economic weight than it needed. Other major powers were inconsistent members: Germany joined late and left early, the Soviet Union came and went, and Japan and Italy eventually exited after clashing with League decisions. With its most influential countries drifting away or ignoring it, the League’s credibility took repeated hits.

As global tensions rose in the 1930s, the League found itself unable to stop aggressive actions. Japan’s invasion of Manchuria in 1931, Italy’s attack on Ethiopia in 1935, and Germany’s increasingly defiant expansion all exposed how powerless the institution was. It could condemn actions, maybe issue sanctions, but without enforcement—no shared military and no unified political will—its warnings didn’t mean much. Countries realized they could ignore the League without serious consequences, and that was basically the beginning of the end.

By the time World War II started in 1939, the League was already irrelevant. It limped along on paper for a few years, but once the fighting broke out, everyone focused on building a new system that wouldn’t repeat the same mistakes. In 1946, the League of Nations officially dissolved, transferring its remaining responsibilities to the newly founded United Nations. In a way, the League served as a prototype—flawed, yes, but crucial—for how the modern world organizes international cooperation today.