As the United States struggled with the Great Depression, Germany and Italy struggled with bitterness and resentment from World War I. In Italy Benito Mussolini gained control of the government and established a fascist dictatorship. In Germany Adolf Hitler and his Nazi Party established a totalitarian state. Germany and Italy formed an alliance that was later joined by Japan. They became known as the Axis Powers. All three nations began to invade or simply annex neighboring countries and territories. Although France and Britain attempted to "appease" Hitler, their efforts were useless. On September 1, 1939, Hitler sent his German armies into Poland. Two days later Britain and France declared war on Germany. World War II had begun.
Hitler employed a blitzkrieg, or "lightning war," to move his armies swiftly throughout most of Europe. Then the German airforce began bombing Britain. The Battle of Britain had begun. Throughout these early years the United States maintained its neutrality. On December 7, 1941, that neutrality ended. The Japanese attacked the American military base at Pearl Harbor, Hawaii. The next day Congress declared war on Japan. Many Americans rushed to sign up for the armed services. Industry mobilized to produce military goods, and Americans everywhere prepared to make sacrifices for the war effort.
The Allies attacked Axis positions in North Africa in November 1942 and were able to turn back the Germans at El Alamein. From there they pushed the Axis out of North Africa and prepared to launch an invasion of Italy. By June 1944 Rome had been liberated. The German defeat at Stalingrad in the winter of 1943 was a major turning point in the war. On June 6, 1944—D-Day—the Allies launched the invasion of Normandy. For the next year they slowly drove German forces back. Germany surrendered unconditionally on May 7, 1945. As the Allies moved across Europe they discovered the horror of the Holocaust—the systematic destruction of Europe's Jews by Hitler and the Nazis.
In the Pacific the United States halted the Japanese advance at the Battle of the Coral Sea and then turned the tide of the war at Midway. From that point the American military pursued a strategy called island hopping to push Japan back. Even faced with certain defeat, Japan refused to surrender and launched attacks by suicide pilots. President Truman decided the time had come to use a new and terrible weapon—the atomic bomb. On August 6, 1945, an American B-29 bomber dropped an atomic bomb on Hiroshima. A second bomb was dropped three days later on Nagasaki. The Japanese government agreed to surrender. World War II, the most destructive conflict in history, was finally over.