The Japanese strategy for expanding their war beyond China can be roughly described as "We can't win in China, so let's fight everybody else." While this doesn't seem entirely rational, the Japanese government and army felt that it was the only alternative to stopping fighting the war in China.

The problem that Japan had in China, with the Second Sino-Japanese War which had started in 1937, was that they hadn't achieved the quick victory they had aimed for. They had captured Beijing and Shanghai, and the capital Nanjing, but the Nationalist government had not surrendered, instead relocating to Chongqing and continuing to fight. Japanese government debt was growing, while Japanese industry was strained to support the war, and there was no end to the war in sight. Japan was still able to buy resources, such as weapons, iron, and oil, from foreign countries into 1940, but as debt grew, this would come to an end. The alternative was to obtain resources through conquest. With the Chinese economy devastated by the war, Japan had no realistic chance to get those resources from China.

The Japanese loss to the Soviet Union in the fighting at Khalkhin Gol/Nomonhan put an end to ambitions to seek those resources in Siberia. The other possibility was SE Asia. By the time the fighting at Khalkhin Gol ended, WWII had begun in Europe, and France and Britain were distracted. Once the German offensive in Western Europe began, things got even better for Japan: the Netherlands (the colonial overlord of Indonesia) was occupied, making Indonesia, and its oil, vulnerable. France was defeated and partly occupied, making French Indo-China vulnerable. Britain was fighting Germany almost alone, making Malaya and Singapore vulnerable.

There was a problem: the US reaction. Japan's foreign goodwill was greatly reduced by the war in China, with widespread condemnation of their aggression (but little concrete action), and by specific incidents such as the Rape of Nanjing. Japan moved to block foreign supplies from reaching China by occupying northern French Indo-China in September 1940. There was little that the French could do; foreign reaction was stronger: the US blocked the sale of scrap iron to Japan.

The German invasion of the Soviet Union in the following June, in 1941, offered new opportunities to Japan. First, it reduced their fear of a Soviet invasion of Manchuria, further reduced by a mutual non-aggression pact with the Soviet Union. This brought immediate military benefit to Japan, as the Soviet Union cut its aid to China. This freed Japanese forces for a move south. Step 1 was to occupy the rest of French Indo-China. The US response was an embargo on oil sales. The Japanese war effort was in crisis: they could not continue to fight for long in China without US oil, or an alternative source of oil. Japan negotiated with the Dutch government-in-exile for access to Indonesian oil, without success. The Japanese government and army had two choices: (1) end the war in China, or (2) take the Indonesian oilfields by force. The latter option would bring war with Britain, and potentially with the US. War with the US would present a serious problem: the Philippines, a US colony, lay between Indonesia and Japan. To have safe access to Indonesian oil, Japan needed to take the Philippines. The pre-war plans for war between the US and Japan over the Philippines, by both countries, featured a Japanese occupation of much of the Philippines followed by a battle between the US and Japanese navies. The naval battle was expected to decide the fate of the Philippines.

The Japanese secret weapons intended to stop the US fleet - the Yamato class battleships - were not yet ready. Yamato was almost-but-not-quite ready (she would be commissioned in December), and the second ship, Musashi, would not be ready until the next year, and the remaining planned ships of the class would take longer. How could the US navy be stopped, in order to secure the Philippines, in order to protect the route to Indonesian oil, in order to sustain the war in China? This was the purpose of the carrier strike on Pearl Harbor: take out the US battlefleet, and the Philippines could be taken and held. The conquest of British SE Asia would give access to tin and rubber from Malaya, eliminate the British base of Singapore, and the conquest of Burma would block supply by land to China.

Contrary to Japanese hopes, the US fought a war of attrition with determination, pulverising the Japanese navy over the next few years. Without at least one of (a) the US agreeing to a quick peace with the Philippines in Japanese hands, (b) successful revolt of India against British rule, or (c) quick victory over China, Japan was going to lose the war. (a) wasn't going to happen, despite Japanese hopes, and neither was (b). Japan had more control over (c), and attempted to knock China out of the war with Operation Ichi-Go, taking place over the latter 2/3 of 1944. China survived, which meant that Japan was going to lose.