The Soviets fight back
After giving ground to early German attacks into the Soviet Union, the Soviets got help from nature by way of intensely harsh weather. One of the earliest, coldest, and snowiest winters in Soviet memory broke over German troops, who didn't have winter equipment because Hitler had expected them to win long before the weather got cold. When the snows hit in November 1941, the Germans were so close to taking Moscow that they actually stole tickets from the end of the Moscow tram line. Their advance was thwarted when the Soviets threw their last fresh troops (who just happened to include Siberian ski troops) into the battle and pushed the Germans away from their capital.
The Germans held on deep in the Soviet Union for another year, but after a heroic defense of the city of Stalingrad in 1942, the Soviets launched a counterattack that destroyed an entire German army. From then on, it was a slow and costly three-year fight to Berlin. The Soviets lost at least 27 million people in World War II, more than 50 times as many people as the U.S. lost. Through 1943, Britain and the United States had lost only a few thousand soldiers in Europe. The Soviets pleaded for a second front in Europe to take some of the pressure off their army.
D-day and Normandy
The Western Allies took two and a half years to launch their D-day invasion; meanwhile they nipped away at the outskirts of Europe. The Allies invaded North Africa in November of 1942, and by the following summer, they'd defeated the German and Italian armies there. Churchill and Roosevelt met in the newly liberated city of Casablanca to plan the rest of the war. The Allies next invaded Italy. Although the Italians were happy to get rid of Mussolini and called their participation in the war quits by September of 1943, the Germans occupied most of the country and fought on in Italy until almost the end of the war.
In June of 1944, the Allies launched a massive invasion of Normandy, France. Over 3 million men had assembled in Britain for the cross-channel push. Thousands died on the beaches, but the Allies pushed inland. A second, smaller invasion came from the south of France. Paris was liberated in August of 1944, and the first major German city fell to the Allies in October.
In the U.S., Franklin Roosevelt won reelection for an unprecedented fourth term as the Allied armies rolled toward victory. Hitler counterattacked at the Battle of the Bulge (1944) in December, but this move merely hastened the end of the war by using up his reserves. By April of 1945, the Soviets and their Western allies were in Berlin, and Hitler had committed suicide. Franklin Roosevelt died of a stroke a few days before the victory.
After Hitler's death, the world began to face the terrible crime of the Holocaust. Six million Jews — almost every Jew the Nazis could find in Europe — had been murdered in cold blood. In addition, Hitler and his willing German and European accomplices had murdered another 5 million political opponents, prisoners of war, Gypsies, Freemasons, disabled children, and Jehovah's Witnesses, among others. Another 3 million Soviet prisoners were starved to death.
The United States struggled with the fact that it had been unwilling to allow refugees from Europe to seek safety in the U.S. before the war. After they knew about the death camps and the killing of families and children, many Americans made a simple pledge: never again. The experience of World War II influences America's international policy to this day.