World War II

The deadliest conflict in human history, fought between 1939 and 1945 across Europe, the Pacific, Africa, and parts of Asia, involving over 30 countries and resulting in an estimated 70 to 85 million deaths. The war ended European colonial dominance, birthed the United Nations, established American and Soviet superpower rivalry, and created the political architecture that governed the world for the next five decades. The Holocaust -- the systematic murder of six million Jews and millions of others -- remains the defining atrocity of the 20th century. Its moral, political, and cultural shadow extends into virtually every contemporary debate about power, genocide, and memory.

Added by @ethanwalsh