World War II, also known as the Second World War, was a global war from 1939 to 1945 in which most of the world's countries, including all the great powers, formed the opposing alliances of the Allies and the Axis. It became a state of total war that directly involved more than 100 million people from over 30 countries, as major participants committed their full economic, industrial, and scientific capabilities and blurred the line between civilian and military resources. It was the deadliest conflict in human history, with 50 to 85 million fatalities, most of them civilians in the Soviet Union and China, and it included massacres, the Holocaust, strategic bombing, premeditated death from starvation and disease, and the only use of nuclear weapons in war. The war began on September 1, 1939, when Germany invaded Poland, followed by France and Great Britain declaring war on Germany on September 3. Germany used blitzkrieg to conquer much of western Europe between May 10 and June 22, 1940, launched the Battle of Britain beginning July 10, and joined Italy and Japan in the Tripartite Pact on September 22. In 1941 Germany and the Axis attacked Russia on June 22 with more than four million troops, and after the Japanese attack on the U.S. Navy at Pearl Harbor on December 7, the U.S. entered the war the next day on the side of the Allies. Major fighting in 1942 and 1943 included the Battle of the Coral Sea, the Battle of Midway, the Guadalcanal Campaign, and the Battle of Stalingrad, which began the German retreat from Russia. In 1944 the Allies invaded France on D-day, fought at Guam, and defeated Germany's final large offensive in the Battle of the Bulge. In 1945 the battles of Iwo Jima and Okinawa were followed by Adolf Hitler's suicide on April 30, Germany's surrender on May 7, the atomic bombings of Hiroshima and Nagasaki on August 6 and 9, and Japan's surrender to U.S. General Douglas MacArthur and the Allies on September 2.