During the Second World War, the China-Burma-India Theater of Operations (CBI) included the territories of East and South Asia: China, Burma, and India. American, British, Indian, and Chinese troops operated in the theater from 1942 to 1945 with Chiang Kai-shek as nominal supreme commander.
The Chinese theater, which was the on-going Second Sino-Japanese War, was important as a means of forcing Japan to devote many resources. Nonetheless, there was little fighting as the nationalist government under Chiang Kai-shek's Kuo-mingtang and the communist insurgents under Mao Zedong conserved their forces; they were as much at war with each other as they were with the Japanese, much to the frustration of the American commander in China, General Joseph Warren Stilwell. The Japanese army in China, however, was far too strong for the weak Chinese armies and never lost a battle to them.
Most of the fighting involving American, British, and/or Indian troops took place in Burma. With the invasion of the Chinese coastline, the taking of principal ports (such as Hong Kong), and the fall of the Malay Peninsula, U.S. supply to China was limited to a single small but treacherous dirt road through the mountains of Burma. To interdict this supply route, the Japanese invaded in 1942 and pushed the British and Colonial armies back into India. British Field Marshal William Slim led British forces to victory in 1944-45.
In late 1944, the Allies formally divided the CBI theater into two theaters China and India-Burma. The British Admiral Lord Louis Mountbatten (1900-79) became supreme commander of the India-Burma theater. Chiang remained supreme commander of the China theater, and Lt. Gen. Albert C. Wedemeyer replaced Stilwell as Chiang's chief of staff and head of American forces in China.
Fighting in this theater continued until the final Japanese surrender in August 1945.
In 1941 the U.S. made a series of decisions to support China in its war with Japan. Lend Lease funds began to flow because President Roosevelt announced the defense of China to be vital to the defense of the United States. Over the summer, as Japan moved south into French Indo-China, the U.S., Britain and the Netherlands slapped an oil embargo on Japan, cutting off 90% of its supplies. The U.S. Army and Navy opposed the move, fearing--correctly--that it would push Japan to war.
Negotiations between the U.S. and Japan went nowhere, as Japan refused to negotiate withdrawal from China. Japan was in China without a declaration of war because of a series of aggressive moves in 1937 by its army commanders in Manchuria; the government in Tokyo had never decided on war but now was so deeply involved it felt it could never go back. Tokyo made the decision in October that a sudden attack to cripple the main American battle fleet at Pearl Harbor would force the Americans to negotiate on more favorable terms. They sank the fleet on December 7, but were astonished that the Americans refused to compromise and instead demanded revenge--and the surrender of Japan.
Rapid Japanese advances, December 1941-March 1942
The amazing speed of the Japanese conquests in 1941-42 stunned the world. It achieved all the goals its "Southern Advance": the conquest of Hong Kong, the Philippines, Malaya and the Dutch East Indies. Britain had decided that Hong Kong was not defensible and pinned its hopes on Singapore, which was defended by two capital ships, five cruisers, nine destroyers, six submarines and 120,000 troops. But in a series of attacks, Japan reduced and eliminated this force. The British fleet was severely defeated when it sortied in late December 1941, and the citadel itself capitulated after many amphibious landing along the Malay Peninsula that surrounded and cut off Singapore.
Britain thereafter placed its forces in India and Ceylon, which themselves became subject to air attacks when the Japanese fleet sailed into the Indian Ocean in early 1942.
Japan forced Thailand to become an ally and easily marched through Malaya, capturing Singapore on February 15. At sea it sank the Asian fleets of the Netherlands and the Royal Navy, and threatened Ceylon and the east coast of India.
Japan was overextended. Its naval base could not defend its conquests, and its industrial base could not beef up the navy. To cut off China from Allied aid, it went into Burma, captured Rangoon on March 8, 1942, cutting the Burma Road lifeline to China. Moving north, the Japanese took Tounggoo, Burma, then captured Lashio in upper Burma on April 29. The British, primarily concerned with India, looked to Burma as the main theater of action against Japan and wanted Chinese troops to fight there.
The United States conjured up visions of millions of Chinese soldiers, who would hold the Japanese then throw them back, while providing close-in airbases for a systematic firebombing of Japanese cities. The overland supply route from India to China had to go through Burma. Chiang realized it was all fantasy. On the other hand, there were vast sums of American dollars available if he collaborated. He did so and managed to feed his starving soldiers, but they were so poorly equipped and led that offensive operations against the Japanese in China were impossible. However, Chiang did release two Chinese armies for action in Burma under Stilwell. They were smashed by the Japanese and Stilwell, on foot, barely escaped to India; the recovery of Burma and construction of the Ledo Road to supply China via Burma became an obsession for Stilwell
Fighting inside China
In 1937 the Japanese seized northern China almost effortlessly, as the Nationalist armies retreated. The capture of the capital at Nanking was marked by one of the horrendous massacres in world history, the "rape of Nanking;" the episode continues to rankle. In December 1937, some 350,000 Chinese soldiers and civilians were slaughtered in an eight-week period, many of them having been raped and/or tortured first.
The Chinese attempted to counterattack at Shanghai, using up hundreds of thousands of their best soldiers in a failed effort. By early 1938 Japan controlled nearly all the main cities, ports and rail lines, as the Nationalists had retreated deep in the mountains, setting up their capital at Chungking (Chongqing). It was repeatedly bombed but held out. One major Japanese offensive was in July, 1938, stopped when the Nationalists blew up the dikes on the Yellow River, costing uncounted numbers of civilian deaths. Finally in late 1938, Japan captured the last important port at Canton, and set up a puppet government at Nanking, the "Reformed Government." Then, after two years, they replaced it with a regime headed by Wang Ching-Wei (Wang Jingwei) (1883-1944). Both collaborationist regimes proved unpopular and incompetent, so Japan had to use its million soldiers to police the hundreds of millions of Chinese it controlled. 
Pushed by the Allies into doing some fighting, the Communists made systematic attacks on Japanese rail lines and garrisons in the "Hundred Regiments offensive" in August-December 1940. The attacks did considerable damage, but the Japanese responded with their "three all" policy: "Kill All, Burn All, Loot All." Three years of massive atrocities followed. After watching the Nationalists destroy the Communist New Fourth Army in January 1941, Mao was careful to keep his forces well away from both the Japanese and the Nationalists.
see Chiang Kai-shek
British Commonwealth forces were also counter-attacking in Burma, albeit with limited success. In August 1943, the Allies formed a new "South East Asia Command" (SEAC) to take over strategic responsibilities for Burma and India from the British India Command, under Wavell. In October 1943, Churchill appointed Admiral Lord Louis Mountbatten as Supreme Allied Commander, SEAC. General William Slim was commander of Commonwealth land forces and directed the Burma Campaign. General Joseph Warren Stilwell commanded U.S. forces in the CBI theater.
In November, 1943 U.S. President Roosevelt, British Prime Minister Winston Churchill, and Chinese leader Chiang Kai-shek met at the Cairo Conference in Egypt, to discuss a strategy to defeat Japan.
In 1944 Japan undertook two major offensives, in Burma and China.
Japan's "Ugo" (U-GO) offensive in March to July 1944 saw 100,000 soldiers in Burma move north to India to capture the airbases supporting China. The "Indian National Army", comprised of Indian prisoners who had switched sides and formed an army that supported Japan, entered the fray. The Japanese besieged British and Indian forces under Lieutenant-General William Slim at Imphal and Kohima, in India. British forces became isolated and their survival depended on British control of the air that allowed airdrops of ammunition and supplies. The British counteroffensive found the Japanese had run out of supplies; many were starving; the Japanese painfully retreated, leaving behind 65,000 dead, half of whom succumbed to disease or starvation.
Japan's Ichigo offensive in China itself was more successful. It began in April 1944 and quickly secured Henan Province and cleared a railroad from Beijing to the central city of Wuhan. They then thrust south, first into Hunan Province and then into the southern provinces of Guangxi and Guizhou, which brought them close to the Nationalist capital of Chongqing. One goal was to secure overland communications to Burma and Thailand. But there was also a political goal. Emperor Hirohito sought to force the U.S. to the negotiating table by significant naval or battlefield victories. He realized Japan could not defeat the Allies, but, underestimating the determination of his angry enemies for a total victory, he thought a substantial victory would strengthen his own position could be secured and that Japan might even retain some of its conquests, including perhaps Manchuria.
see Clair Chennault
Flying the Hump
The trans-Himalayan airlift, the "Hump," was the first sustained and most ambitious combat airlift operation in modern history. Cobbled together with only a handful of airplanes and aircrews in early 1942, the operation grew to become the ultimate expression of American commitment to keeping China in the war and using its airfields to attack Japan. In all it delivered 740,000 tons of cargo, flying in some of the world's worst weather system and over its most rugged terrain, all the while under the threat of enemy attack.
The Hump airlift was initially started to serve as a display of American support for its Chinese ally who had been at war with Japan since 1937. Motivations behind the airlift's execution changed during the war. Once the US entered the war, the Hump was seen as an extension of its (pre-December 1941) Lend-Lease aid to China, aid that had previously been delivered over the Burma Road, but that route was cut off by the Japanese in the spring of 1942. The airlift became the only means to supply China and "keep China in the war." To the US, China's national will was tottering as a result of its brutal war with Japan since 1937, and the influx of US material over the Himalayas was the best way to prevent Chinese capitulation.
By late 1943 the airlift became the centerpiece of US strategy focused on the destruction of Japan. The Hump would enable China-based B-29 bombers to begin striking the Japanese home islands, which supposedly were made of such fragile paper-and-wood construction they would easily burn down. Second, the airlift delivered a stockpile of supplies in preparation for the planned Army invasion of Japan. Hump tonnage skyrocketed in 1944-45 because of the growth of its infrastructure that included a robust air traffic control system, innovative maintenance procedures, dozens of navigation aid-equipped airfields, hundreds of airplanes, and thousands of pilots. All of this combined to dwarf tonnage delivered to China on land routes, ushering in a paradigm shift in the history of wartime logistics that saw airlift become the most efficient and durable means of supply.
By the start of 1944, as the airlift's capability soared, American strategists moved beyond a concern for Chinese national will and used the airlift as the primary means of supplying American forces in China in preparation for the final assault on Japan. Strictly from the standpoint of war materiel, the airlift set the preconditions that had to be met to make possible all other allied military action, and dictated the level of effort the Americans could bring to bear against the Japanese, being the sole route to China until early 1945, when the Ledo Road opened. Other routes were discussed and attempted, but in the end the only way for supplies to get into China was over the Himalayas. In addition to being an enabler, the airlift was also a driver of CBI strategy, as it was an expression of the broader airpower orientation of the theater. Difficult terrain, extreme weather, and primitive roads all combined to make the CBI a theater best traversed by air. It was in the CBI, and only in the CBI, that allied troops were most commonly inserted, supplied, and extracted by air.
Historiography and memory
The CBI theater has not been as widely researched or as a popular topic as other aspects of World War II. largely ignored by historians, apart from the outstanding 3-volume official histories by Charles F. Romanus and Riley Sunderland produced what is probably the canonical account of the theater (3 vols., 1953-58). Barbara Tuchman won the 1972 Pulitzer Prize in history for her biography of Stilwell (Stilwell and the American Experience in China, 1911-45 [Macmillan, 1970]). In popular culture, the CBI Theater was the context for the Oscar-winning The Bridge on the River Kwai (1957). The Japanese for the first few generations after the war were reluctant to address the war years. In China, war memories of massacres, especially the Nanjing Massacre and hardships, remained all too vivid. In international politics, China continues to use its war experience in an effort to pressure Japan into making some sort of apology for the war.
- Iris Chang, The Rape of Nanking: The Forgotten Holocaust of World War II, (1998) excerpt and text search
- David P. Barrett and Larry N. Shyu, eds. Chinese Collaboration with Japan, 1932–1945: The Limits of Accommodation (2001) excerpt and text search.
- Wang Ke-wen, "Battle of Hundred Regiments" in Wang, ed. Modern China: An Encyclopedia of History, Culture, and Nationalism (1998) online p. 19; Samuel B. Griffith II, The Chinese People's Liberation Army (1967)
- Edward J. Drea, In the Service of the Emperor: Essays on the Imperial Japanese Army (1998), p. 188
- See John D. Plating, "Keeping China in the War: The Trans-Himalayan `Hump' Airlift and Sino-US Strategy in World War II." PhD dissertation Ohio State U. 2007.
- The Bridge on the River Kwai (1957). British Film Institute. Retrieved on 3 November 2013.
- La Robert S. Forte, and Ronald E. Marcello. Building the Death Railway: The Ordeal of American POWs in Burma, 1942-1945. (1993).
- Rana Mitter, "Remembering the Forgotten War," History Today 55, no. 8 (2005): 17-19.
- Rana Mitter, "Old Ghosts, New Memories: China's Changing War History in the Era of Post-Mao Politics." Journal of Contemporary History 38, no. 1 (2003): 117-131.