I've never understood what Japan had against China, Burma, Singapore, etc., that warranted such brutality and military aggression in the 1930s. It had to have been more than territorial disputes or a struggle for resources, and Japan wasn't really being threatened or oppressed by all of these neighbor states. It just seems counterintuitive to me considering the isolationism of Japan in the 19th century up until their war with Russia in 1904.
Japan's military adventures in Asia were a direct result of the growing power of the military in the late 20s and early 30s.
Japan's military was founded on French model, but this was very quickly changed to a Prussian model and the Japanese system of government followed suit with the Meiji constitution. The Meiji Constitution made the civilian government and the military separately accountable to the Japanese Emperor. In reality, the Emperor very rarely involved himself in the running of the country and his role was mostly to resolve disputes between different parts of the government. The important part here is that the military had no direct legal requirement to listen to the orders of the elected civilian government. The civilian government could still exercise a great deal of control over the military using other measures, but as we shall see the military was in general invested with too much power.
The Father of the Imperial Military, Yamagata Aritomo, set up this system for two reasons. First, Prussia was the most powerful land power in Europe at the time and Japan wanted to emulate success. Secondly, he wanted to limit the ability of money-grubbing or partisan politicians from interfering with the military. He saw the role of the military as being outside the scope of politicians.
The early military adventures of Japan had mixed results at best. You mentioned in your post that Japan remained isolated until the Russo-Japanese war but this isn’t really true. The country had opened up to the West fully in the 1850s and had begun engaging in foreign expeditions as early as 1874, when Japan launched a punitive campaign against Taiwan after some locals slaughtered stranded Japanese fishermen. The Japanese force of 3,600 men fought one victorious battle with the locals and killed about 30 of them. More than 500 of the Japanese soldiers died of disease. So yeah, mixed results. Still, the expedition was nominally a success and Japan forced Qing China to pay a small fine for the deaths of the Fishermen before withdrawing. The Imperial Military saw action again, in a more important campaign in 1875.
Japan had long traded extensively with Korea, even during the otherwise closed off Edo Period, and this continued through the Meiji Restoration and the Westernization of Japan. However, as Japan became more Western, many in the country felt that it should adopt the policies of the Imperial Western Powers it was emulating. Korea granted special (unequal) trade rights to European powers and now that Japan was becoming more westernized, it was felt that Japan should “protect” its merchants in Korea as well. So in 1875, the Japanese deliberately manufactured an international incident on an island off the Korean coast. A Japanese Navy Ship landed on the island without telling the Koreans beforehand, ostensibly to collect water, and the Korean garrison opened fire. Japanese Marines landed on the island and engaged the Korean garrison and the resulting battle was a draw. However, Korea was sufficiently cowed by Japan’s military to agree to grant Japan the same special trade rights it was granting Europeans, which included extraterritoriality for Japanese citizens and freedom to conduct business without interference from the Korean government. This was Japan’s first real Imperial foray, and it’s the first sign that Japan is truly becoming a world power.
Continued in the next post...
Of the countries you mention, Japan only invaded China prior to WWII. Singapore was a British colony, Burma was a British colony, and so forth. The other countries that Japan attacked prior to WWII were Korea, Russia, and Taiwan.
The hallmark of a Great Power at the time was to have a large colonial base. One need only look at the British Empire and its global reach to see how colonies were viewed. As such, Japan desired colonies of its own. Korea was an easy target, being near Japan. Historically, Japan had invaded Korea in the 1600s (although the invasion was repulsed due to the efforts of the Korean Navy, the Ming Dynasty intervention, and dissent among the Japanese retainers). In a series of wars with China and Russia, Japan was able to establish control of Korea, formally annexing it in the early 1900s.
The Japanese at the time were not interested in assimilating the Koreans. Instead, the policy was that Koreans, having been conquered by Japan, were inferior as a result. To help solidify their hold on Korea, as well as provide a stronger workforce for economic benefit, Japan introduced public education in Korea, and revived the old Korean alphabet. These were all done to indoctrinate the Korean populace into accepting subordination under Japan, and to make Korea a useful colony.
After World War I, where Japan was on the victorious Entente, they had hoped to acquire Germany's colonies in the Pacific. Instead, they were only given the colonies north of the equator, which basically amounted to the treaty port of Shandong and a few minor concessions in other cities. They were rather displeased by this, especially as Britain and France were gouging themselves on German colonies.
Then, during a meeting to discuss the League of Nations, Japan proposed a racial equality clause. The idea behind the clause was so that Japan would be recognized as an equal among the Western powers. However, this proposal would also have massive ramifications for European powers, as it would seriously threaten the legitimacy of their colonial rule. It was rejected by the US and the UK (mostly due to Australian resistance), and as a result, which infuriated the Japanese, as they interpreted it to mean a Western refusal to acknowledge them as equals.
The Washington Naval Treaty also further alienated the Japanese. The naval limits dictated by the treaty were in a 5:5:3 ratio for the US, UK< and Japan, respectively. Japan further saw this as an example of them being snubbed, which caused strong anti-Western attitudes among the public, especially in the military.
Military hotheads soon started popping up, assassinating many prominent industrialists and politicians. The military was going out of control. Many younger officers sought to unite Asia under Japan, forming a strong power bloc against the West. A pair of rather junior officers independently launched an attack on Manchuria without the knowledge of the Japanese government (or for that matter, the Japanese high command), and by the time anybody was in a position to do anything in what became known as the Mukden incident, Manchuria had fully fallen to Japanese control. The culminating factor was the assassination of Prime Minister Inukai in the May 15 incident. Inukai was one of the last prime ministers to resist the military. Afterwards, the military was able to gradually assume control of the government.
Ethnic tensions between Chinese and Japanese in China provided Japan an excuse to intervene in China. These incursions culminated in the Marco Polo Bridge incident, which despite efforts by the civilian governments rapidly escalated into full-blown war.