Having already terrorized and destroyed areas of mainland China before the push to take over other territories in Southeast Asia, Japan began a diplomatic campaign to secure allies. In September 1940, Germany, Italy, and Japan became allies under the Tripartite Pact. As Japan worked to increase its imports through economic agreements with French and Dutch colonies, the United States, Great Britain, and the Netherlands began embargo of gasoline, aviation gas, scrap metal, steel and other essential building materials.
After the Japanese attack on Pearl Harbor, the U.S., United Kingdom and other Allies declared war on Japan. The war spread throughout the Pacific region as Japan had initial success in its military campaign. However, in 1943 the hard-fought campaigns at the battles of Buna-Gona, the Tarawa, the Philippine Sea, Leyte Gulf, Iwo Jima, Okinawa, and others resulted in horrific casualties, mostly on the Japanese side, and produced further Japanese retreats.
On August 6 and August 9, 1945, the U.S. dropped two atomic bombs on Hiroshima and Nagasaki. An estimated 150,000–246,000 people died as a direct result of these two bombings, during which the Soviet Union entered the war against Japan. Japan surrendered on August 15, 1945, and a formal Instrument of Surrender was signed on September 2, 1945, on the battleship USS Missouri in Tokyo Bay. The surrender was accepted, from a Japanese delegation led by Mamoru Shigemitsu, by General Douglas MacArthur, as Supreme Allied Commander, along with representatives of each Allied nation.
Over the course of the war, Japan displayed many significant advances in military technology, strategy, and tactics. Among them were the Yamato-class battleship, the Sen-Toku submarine bomber carriers, the Mitsubishi Zero fighters, and Kamikaze bombers.