In September 1939, Germany invaded Poland from the west, while the Soviet Union invaded from the east. Britain and france responded by declaring war on Germany and World War II began in Europe.

On the morning of December 7, 1941, two seperate waves of Japanese airplanes attacked the U.S. Pacific fleet stationed in Pearl Harbor, Hawaii. The suprise attack destroyed six ships and 180 aircrafts, took the lives of 2,403 Americans, and wounded 1,178 others.

American and Japanese aircraft carriers fought one another in the Battle of the Coral Sea. It was the first time in history that aircraft carriers fought while seperated by more than 100 miles of ocean. Planes from each side flew and attacked the other side's ships. Japanese bombers sank one American aircraft carrier and severely damaged a second.

In June 1942, the Japanese attempted to lure the U.S. Pacific fleet into a trap near the island of Midway. Their aim was to destroy all U.S. aircraft carriers operating in the Pacific and to capture the U.S.  naval base on Midway. The Americans had deciphered part of the Japanese secret naval code and knew that they were planning a major attack on Midway.U.S. Admiral Chester Nimitz assembled several carriers and had rapid repairs made to the carrier that had been damged at the Battle of the Coral Sea. The American carriers moved into position just northeast of Midway Island without detection. The Japanese began their attack not knowing that the U.S. Navy was nearby. Just when the Japanese carriers were least defensible, American dive-bombers suddenly appeared in the sky and bombed their decks. The Japanese lost four large aircraft carriers, while the Americans lost only one. The Battle of Midway was the turning point of the war in the Pacific.

American and British troops began preparing for a massive amphibious invasion of France, known as "Operation Overlord." General Dwight D. Eisenhower was placed in supreme command of the Allied invasion.  Large numbers of men, tanks, motorized troop carriers, and artillery gathered in Britain. Allied airplanes conducted bombing missions night and day to weaken German positions. The western allies even took steps to fool the German army into thinking their main assault would be farther north at Calais. Bad weather delayed the launching of the invasion. On "D-Day", June 6, 1944, more than 4,400 ships and other landing crafts crossed the English Channel to bring Allied troops to the beaches of Normandy, France.

Hitler committed suicide at his underground buker in Berlin on April 30, and Germany's military leaders surrendered to the Allies on May 7-8 known as V-E Day.

On August 6, the first atomic bomb was exploded over Hiroshima. Three days later a second bomb was exploded over Nagasaki. As many as 100,000 people were killed in each explosion. Each city was totally destroyed. Japan surendered on V-J Day, just after the second explosion, once the United States agreed to permit the Japanese Emperor to remain on his throne.