The Southeast Asian Theatre of World War II was a brutal military campaign that lasted directly after the Japanese attack on Pearl Harbor on December 8th, 1941, to the Japanese surrender on September 2nd, 1941.
The Southeast Asian Theatre was notorious for its harsh tropical climate that effected the combined armed military armies of the Republic of China (ROC), the United Kingdom (UK), and the United States (US) (although other nations such as Australia also offered military support) against the Imperial Japanese military, which had dug into the region in an extremely quick fashion. The Japanese proceeded to invade and successfully taking over the countries and territories of Burma (now known as Myanmar), Thailand, French Indochina (now known as the countries Vietnam, Laos, and Cambodia), Malaya (now known as Malaysia), Singapore, Ceylon (now known as Sri Lanka), the Dutch East Indies (now known as Indonesia), Hong Kong, and the Philippines.
The allies suffered devastating defeats in the beginning of the long campaign, which included the Indian Ocean Raid, in which the Japanese Navy destroyed most of the British far East fleet, and forced the British Navy to India to conduct military engagements. In addition, the British surrender in Singapore is known as the largest British defeat in history, and marked the end of effective battleship combat.
The United States, in addition, suffered defeats all over the Pacific, from the Japanese invasion of the Philippines, and the Japanese invasions of several US bases throughout the Pacific region. However, the Japanese victory spree would come to an end on June 7th, 1942, with the Battle of Midway, in which US naval forces successfully defeated the Japanese naval fleet consisting of four of the fastest aircraft carriers of the time, which served as a devastating blow for the Japanese military, and one they could not recover from.
However, in Southeast Asia, the allies were facing several main deficits: while the United States was busy in the eastern Pacific regaining lost ground taken by the Japanese, the combined forces of ROC and the UK were facing the problem of supply shortages, which led to the spread of many diseases like cholera, dysentery, and malaria. The Japanese, however, even with their navy on its backfoot, were supplied with sufficient resources to continue their conquests, in which they sought to move from Southeast Asia to India, hoping to start a rebellion that would topple British control of the country. In addition, the ROC were still occupied with battling against the Japanese in mainland China, in which the Chinese had been able to resist the Japanese since the beginning of the Second Sino-Japanese War in 1937, a remarkable feat considering the political state of China at the time. The UK, on the other hand, were occupied with German expansion across Europe and into North Africa, and were stretched thin in order to reinforce their armies in Southeast Asia.
However, the allies were saved in 1944 with Operation Overlord, better known as ‘D-Day’. With the amphibious invasion of continental Europe a success, the allies could focus more supplies on the Pacific War, and in the same year the British launched several successful naval attacks against Japanese oil refineries in Sumatra, inflaming Japanese oil shortages, and blocking Japan from sufficiently supplying their forces in the Eastern Pacific against the US.
Thus, the Japanese, unable to sufficiently supply their own troops and reinforce their military conquest, went into recluse, in which, their staunch defensive stance throughout the rest of the war would prove their downfall. The Japanese fleet was almost completely shattered at the Battle of the Philippine Sea in 1944, and the successful US invasion of the Philippines pushed the Japanese back toward their home islands. The campaign farther west in mainland Southeast Asia was going exceedingly well for the allies, and Chinese and British forces were able to apply enough pressure on Japan in the Southeast Asian theatre that the Japanese switched all resources into protecting the islands of Okinawa and Iwo Jima, each of which they lost to allied forces. The Japanese, unable to sustain themselves any longer, and after frequent air raids and bombings which culminated in the US dropping two atomic bombs on Hiroshima and Nagasaki, surrendered on September 2nd, 1945, officially ending the Pacific Theatre and World War II as a whole.