World War I ended in 1918 with a peace treaty so brutal it felt less like diplomacy and more like revenge. Germany was blamed for everything, stripped of territory, and forced to pay reparations so massive they weren't fully paid off until 2010. Yes, 2010. The victors thought they were punishing Germany. What they actually did was plant a seed of rage that would grow into something far worse than the war they'd just survived.

Into that rage stepped Adolf Hitler. He didn't seize power through a coup — he was voted in. Germany in the early 1930s was economically destroyed, politically humiliated, and desperate for someone to blame and someone to follow. Hitler offered both. He blamed Jewish people, communists, and foreign powers for Germany's suffering. He promised national rebirth, military strength, and greatness. And millions of people, many of them ordinary, educated, and not cartoonishly evil, said yes. That's the part history classes tend to skip over. Fascism didn't win by hiding what it was. It won because enough people wanted what it was selling.

Germany wasn't alone. Italy under Mussolini and Japan under a militarist government were also pursuing aggressive expansion. When Germany invaded Poland in September 1939, Britain and France finally said enough — and declared war. What followed was a global conflict fought on six continents, from the beaches of Normandy to the jungles of the Pacific to the deserts of North Africa. The scale is almost impossible to absorb. The Soviet Union alone lost an estimated 27 million people. The United States, which entered after Japan bombed Pearl Harbor in December 1941, mobilized 16 million soldiers. Every major economy on earth was redirected toward killing.

The war ended in two stages. Germany surrendered in May 1945 after Soviet forces reached Berlin and Hitler died by suicide in his bunker. Japan surrendered in September 1945 — but only after the United States dropped atomic bombs on Hiroshima and Nagasaki, killing an estimated 110,000 to 210,000 people instantly and through radiation. The debate over whether that decision was justified still runs hot among historians. What's not debated: it changed warfare forever. Humanity had built a weapon capable of ending civilization, and it had already used it.