War breaks out in the Pacific (1941)
In 1939 the United States had renounced its trade treaty with Japan and beginning with an aviation gasoline ban in July 1940 Japan had become subject to increasing economic pressure. During this time, Japan launched its first attack against Changsha, a strategically important Chinese city, but was repulsed by late September. Despite several offensives by both sides, the war between China and Japan was stalemated by 1940. In order to increase pressure on China by blocking supply routes, and to better position Japanese forces in the event of a war with the Western powers, Japan had occupied northern Indochina Afterwards, the United States embargoed iron, steel and mechanical parts against Japan. Other sanctions soon followed.
In August of that year, Chinese communists launched an offensive in Central China; in retaliation, Japan instituted harsh measures (the Three Alls Policy) in occupied areas to reduce human and material resources for the communists. Continued antipathy between Chinese communist and nationalist forces culminated in armed clashes in January 1941, effectively ending their co-operation. In March, the Japanese 11th army attacked the headquarters of the Chinese 19th army but was repulsed during Battle of Shanggao. In September, Japan attempted to take the city of Changsha again and clashed with Chinese nationalist forces.
German successes in Europe encouraged Japan to increase pressure on European governments in south-east Asia. The Dutch government agreed to provide Japan some oil supplies from the Dutch East Indies, but negotiations for additional access to their resources ended in failure in June 1941. In July 1941 Japan sent troops to southern Indochina, thus threatening British and Dutch possessions in the Far East. The United States, United Kingdom and other Western governments reacted to this move with a freeze on Japanese assets and a total oil embargo.
Since early 1941 the United States and Japan had been engaged in negotiations in an attempt to improve their strained relations and end the war in China. During these negotiations Japan advanced a number of proposals which were dismissed by the Americans as inadequate. At the same time the US, Britain, and the Netherlands engaged in secret discussions for the joint defence of their territories in the event of a Japanese attack against any of them. Roosevelt reinforced the Philippines (an American possession since 1898) and warned Japan that the US would react to Japanese attacks against any "neighboring countries".
Frustrated at the lack of progress and feeling the pinch of the American-British-Dutch sanctions, Japan prepared for war. On 20 November it presented an interim proposal as its final offer. It called for the end of American aid to China and the supply of oil and other resources to Japan. In exchange they promised not to launch any attacks in Southeast Asia and to withdraw their forces from their threatening positions in southern Indochina. The American counter-proposal of 26 November required that Japan evacuate all of China without conditions and conclude non-aggression pacts with all Pacific powers. That meant Japan was essentially forced to choose between abandoning its ambitions in China, or seizing the natural resources it needed in the Dutch East Indies by force; the Japanese military did not consider the former an option, and many officers considered the oil embargo an unspoken declaration of war.
Japan planned to rapidly seize European colonies in Asia to create a large defensive perimeter stretching into the Central Pacific; the Japanese would then be free to exploit the resources of Southeast Asia while exhausting the over-stretched Allies by fighting a defensive war. To prevent American intervention while securing the perimeter it was further planned to neutralise the United States Pacific Fleet and the American military presence in the Philippines from the outset. On 7 December (8 December in Asian time zones), 1941, Japan attacked British and American holdings with near-simultaneous offensives against Southeast Asia and the Central Pacific. These included an attack on the American fleet at Pearl Harbor, landings in Thailand and Malaya and the battle of Hong Kong.
These attacks led the United States, Britain, China, Australia and several other states to formally declare war on Japan, whereas the Soviet Union, being heavily involved in large-scale hostilities with European Axis countries, preferred to maintain a neutrality agreement with Japan. Germany, followed by the other Axis states, declared war on the United States in solidarity with Japan, citing as justification the American attacks on German submarines and merchant ships that had been ordered by Roosevelt.
Axis advance stalls (1942–43)
In January, the United States, Britain, Soviet Union, China, and 22 smaller or exiled governments issued the Declaration by United Nations, thereby affirming the Atlantic Charter, and agreeing to not to sign separate peace with the Axis powers.
During 1942 Allied officials debated on the appropriate grand strategy to pursue. All agreed that defeating Germany was the primary objective. The Americans favoured a straightforward, large-scale attack on Germany through France. The Soviets were also demanding a second front. The British, on the other hand, argued that military operations should target peripheral areas in order to throw a "ring" around Germany which would wear out German strength, lead to increasing demoralisation, and bolster resistance forces. Germany itself would be subject to a heavy bombing campaign. An offensive against Germany would then be launched primarily by Allied armour without using large-scale armies. Eventually, the British persuaded the Americans that a landing in France was infeasible in 1942 and they should instead focus on driving the Axis out of North Africa.
At the Casablanca Conference in early 1943 the Allies issued a declaration declaring that they would not negotiate with their enemies and demanded their unconditional surrender. The British and Americans agreed to continue to press the initiative in the Mediterranean by invading Sicily to fully secure the Mediterranean supply routes. Although the British argued for further operations in the Balkans to bring Turkey into the war, in May 1943 the Americans extracted a British commitment to limit Allied operations in the Mediterranean to an invasion of the Italian mainland and to invade France in 1944.
By the end of April 1942, Japan and its ally Thailand had almost fully conquered Burma, Malaya, the Dutch East Indies, Singapore, and Rabaul, inflicting severe losses on Allied troops and taking a large number of prisoners. Despite stubborn resistance at Corregidor, the US possession of the Philippines was eventually captured in May 1942, forcing its government into exile. On 16 April, in Burma 7,000 British soldiers were encircled by the Japanese 33rd Division during the Battle of Yenangyaung and rescued by the Chinese 38th Division. Japanese forces also achieved naval victories in the South China Sea, Java Sea and Indian Ocean, and bombed the Allied naval base at Darwin, Australia. The only real Allied success against Japan was a Chinese victory at Changsha in early January 1942. These easy victories over unprepared opponents left Japan overconfident, as well as overextended.
In early May 1942, Japan initiated operations to capture Port Moresby by amphibious assault and thus sever communications and supply lines between the United States and Australia. The Allies, however, prevented the invasion by intercepting and defeating the Japanese naval forces in the Battle of the Coral Sea. Japan's next plan, motivated by the earlier Doolittle Raid, was to seize Midway Atoll and lure American carriers into battle to be eliminated; as a diversion, Japan would also send forces to occupy the Aleutian Islands in Alaska. In early June, Japan put its operations into action but the Americans, having broken Japanese naval codes in late May, were fully aware of the plans and force dispositions and used this knowledge to achieve a decisive victory at Midway over the Imperial Japanese Navy.
With its capacity for aggressive action greatly diminished as a result of the Midway battle, Japan chose to focus on a belated attempt to capture Port Moresby by an overland campaign in the Territory of Papua. The Americans planned a counter-attack against Japanese positions in the southern Solomon Islands, primarily Guadalcanal, as a first step towards capturing Rabaul, the main Japanese base in Southeast Asia.
Both plans started in July, but by mid-September, the Battle for Guadalcanal took priority for the Japanese, and troops in New Guinea were ordered to withdraw from the Port Moresby area to the northern part of the island, where they faced Australian and United States troops in the Battle of Buna-Gona. Guadalcanal soon became a focal point for both sides with heavy commitments of troops and ships in the battle for Guadalcanal. By the start of 1943, the Japanese were defeated on the island and withdrew their troops. In Burma, Commonwealth forces mounted two operations. The first, an offensive into the Arakan region in late 1942, went disastrously, forcing a retreat back to India by May 1943. The second was the insertion of irregular forces behind Japanese front-lines in February which, by the end of April, had achieved mixed results.
Eastern Front (1942–43)
Despite considerable losses, in early 1942 Germany and its allies stopped a major Soviet offensive in Central and Southern Russia, keeping most territorial gains they had achieved during the previous year. In May the Germans defeated Soviet offensives in the Kerch Peninsula and at Kharkiv, and then launched their main summer offensive against southern Russia in June 1942, to seize the oil fields of the Caucasus and occupy Kuban steppe, while maintaining positions on the northern and central areas of the front. The Germans split Army Group South into two groups: Army Group A struck lower Don River while Army Group B struck south-east to the Caucasus, towards Volga River. The Soviets decided to make their stand at Stalingrad, which was in the path of the advancing German armies.
By mid-November, the Germans had nearly taken Stalingrad in bitter street fighting when the Soviets began their second winter counter-offensive, starting with an encirclement of German forces at Stalingrad and an assault on the Rzhev salient near Moscow, though the latter failed disastrously. By early February 1943, the German Army had taken tremendous losses; German troops at Stalingrad had been forced to surrender, and the front-line had been pushed back beyond its position before the summer offensive. In mid-February, after the Soviet push had tapered off, the Germans launched another attack on Kharkiv, creating a salient in their front line around the Russian city of Kursk.
Western Europe/Atlantic & Mediterranean (1942–43)
Exploiting poor American naval command decisions, the German navy ravaged Allied shipping off the American Atlantic coast. By November 1941, Commonwealth forces had launched a counter-offensive, Operation Crusader, in North Africa, and reclaimed all the gains the Germans and Italians had made. In North Africa, the Germans launched an offensive in January, pushing the British back to positions at the Gazala Line by early February, followed by a temporary lull in combat which Germany used to prepare for their upcoming offensives. Concerns the Japanese might use bases in Vichy-held Madagascar caused the British to invade the island in early May 1942. An Axis offensive in Libya forced an Allied retreat deep inside Egypt until Axis forces were stopped at El Alamein. On the Continent, raids of Allied commandos on strategic targets, culminating in the disastrous Dieppe Raid, demonstrated the Western Allies' inability to launch an invasion of continental Europe without much better preparation, equipment, and operational security.
In August 1942, the Allies succeeded in repelling a second attack against El Alamein and, at a high cost, managed to deliver desperately needed supplies to the besieged Malta. A few months later, the Allies commenced an attack of their own in Egypt, dislodging the Axis forces and beginning a drive west across Libya. This attack was followed up shortly after by Anglo-American landings in French North Africa, which resulted in the region joining the Allies. Hitler responded to the French colony's defection by ordering the occupation of Vichy France; although Vichy forces did not resist this violation of the armistice, they managed to scuttle their fleet to prevent its capture by German forces. The now pincered Axis forces in Africa withdrew into Tunisia, which was conquered by the Allies in May 1943.
In early 1943 the British and Americans began the "Combined Bomber Offensive", a strategic bombing campaign against Germany. The goals were to disrupt the German war economy, reduce German morale, and "de-house" the German civilian population.