Thanks very much to /u/Starwarsnerd222 for covering the philosophical underpinnings as well as the mechanics of the Greater East Asia Co-Prosperity Sphere (大東亜共栄圏). As they said, I will be focusing more on the political undercurrents of Japanese policy from the end of World War I, up through the beginning of the Second Sino-Japanese War, with a brief aside on the descent of Japan into war with the West. Suffice it to say, Japan's plans for itself going forward depend greatly on when you look.

While Japan was not directly involved with the worst of the fighting in World War I, the conflict did have a deep impact on Japanese planners as they looked to the future.^1 Prior to World War I, Japanese planners had considered that future wars would be much like their previous victories over China and Russia in the First Sino-Japanese and Russo-Japanese Wars. Namely, that the conflict would be relatively short, and that there would be neutral powers out in the world. This meant that despite Japan's lack of natural resources in the Home Islands, Japan could rely on foreign imports to keep its war industry going, while also relying on foreign financing to fund those same imports, and a short war would be decided by how quickly Japan could mobilise and attack. Japan had focused its industrial growth on acquiring the heavy industry it needed to build its own guns, artillery, and warships, while relying on foreign sourced raw materials to fuel those same industries.

World War I destroyed these notions.

Japan saw what was arguable the greatest industrial power in Europe, the German Empire, ground down over a long war. The vast German war industry had been ground to a nub, deprived of raw materials by the British blockade, and the war had no neutral powers of consequence. Studying the conflict, the Army Ministry came to a worrying conclusions: the Japanese empire, as it was with the Japanese Home Islands, Korea, Formosa, Sahkalin, and assorted smaller island possessions, lacked the resources for sustaining total war. If Japan wanted to be able to sustain itself in a future war, it would need territories with richer resources, and China represented was a key potential target, with Manchuria a tempting first target. When the warlord Zhang Zuolin seemed to be leaning away from Tokyo, officers of the Kwantung Army had him assassinated and later invaded Manchuria. This was done as part of a drive to secure autarky for Japan. Despite being unsanctioned by Tokyo, and very concerning to those within the Army who sought preparation for total war, the Manchurian Incident had broad support, as it gave Japan access to substantial new resources, and provided a foothold for further Japanese economic expansion into even more resource rich northern China.

At this point, it's necessary to discuss the fractious nature of Japanese decision making. It is exceptionally difficult to speak of "Japanese" policy and goals, as there was often little done to co-ordinate policy at the highest levels. Staff officers in Tokyo could be working at cross-purposes to field officers in the Kwantung Army, all while the civilian government attempted to develop its own goals. Add the Navy with its own interests into the mix, and we find a situation where there was effectively no true central planning for any one particular goal. To give an example an army conference in 1933 saw a conflict between so-called "total war" officers led by Colonel Nagata Tetsuzan of the Military Affairs Section of the Army Ministry and those of the Kōdōha faction, led by War Minister General Araki Sadao. Araki pushed for a crash mobilisation plan, aiming at creating large army that would be ready for war with the Soviet Union in 1936, while Nagata argued for a conservation of resources and a development of Japan's industrial base over a longer period of time. Meanwhile, the Navy was also involved in its own factional dispute between Fleet and Treaty Faction officers, with the latter being supporters of the 1922 Washington Naval Treaty and the former opponents of the same. By 1933, the Fleet Faction had come to dominance and was more supportive of Araki's army expansion plans, so long as the Navy received a larger share of the budget to continue expanding the fleet. Despite this, the Army in general was aimed at war with the Soviet Union, which the Navy viewed with great suspicion, and the Navy was determined that it would not allow itself to be sidelined by enabling Japanese policy to be directed solely against the Soviet Union. Preparation for war against the US and Britain would afford the Navy a far larger role, and a commensurately larger share of national resources. This inherent contradiction in goals would never be satisfactorily addressed, and it tended to result in the Army wanting enough resources to fight the Soviet Union, while the Navy wanted the resources to fight the United States. This led to plans which almost seemed to call for Japan simultaneously sinking American warships and importing American machine tools. There was simply no body in Japan that would be capable of bringing either the Army or Navy to heel, and squaring the circle of Japanese Imperial Defence. Both the Army and Navy would have to be satisfied.

This has necessary consequences for the question of what Japan's long term plans were. The total war officers--who were in the ascendancy within the Imperial Army by 1934, and especially with the purge of the Kōdōha faction which followed the February 26 Incident--wanted at least 5 years of sustained peace in order to dramatically expand Japan's war industry, with the end goal of being able to fight a protracted war with the Soviet Union. To that end, the total war officers wanted to pursue a course of rapprochement with Chiang Kai-shek and the United States, focusing Japan's war effort wholly on the Soviet Union. Their vision of the future was for Japan to be oriented northward, with extensive economic concessions in northern China, but avoiding hostility with Nanjing. However, despite achieving a great deal of support in the War Ministry and even amongst the civilian government, the plan was not exactly universally supported. The Navy, of course, remained staunchly imposed, and wanted the main focus to be pointed southward at the European colonies in Asia and the United States, as that was what would justify the Navy's ambitious expansion program. Regardless, in 1937, the new Cabinet led by Prince Konoe Fumimaro had agreed to push through an ambitious economic expansion plan that formed the base of the total war officer's dreams of autarky. The plan was to be sent to the Diet on 23 July, 1937. The Marco Polo Bridge incident occurred on 7 July, and permanently derailed the plans of the total war officers.

The war in China was a complete disaster for any plans for Japanese autarky. Not only did it destroy any possibility of a positive relationship with Nanjing, but it began to dramatically sour relations with the United States, the nation with which Japan was likely the most dependent on for the imports of both raw materials and capital goods it needed to achieve the dreamed of economic expansion. However, the war in China quickly sucked up much of the resources that had been earmarked for industrial expansion via war needs. At this point, Japanese policy began to become highly reactive, and ultimately dominated by the war in China. As Chiang Kai-shek continued to refuse to accept Japanese terms that would give it deep economic influence across China, the drain on resources prevented substantial economic expansion in Japan, and the new goal became trying to seek a way to compel China's collapse. This was what led to the series of dominoes that ultimately would culminate in Japan's decision to go to war with the United States, in order to secure the resources Japan needed to adequately finish the war in China.

I hope this has helped further elucidate your question, and please feel free to ask any follow ups.

Sources

• Michael A Barhnart, Japan Prepares for Total War: The Search for Economic Security, 1919-1941

• Edward J Drea, Japan's Imperial Army: Its Rise and Fall, 1853-1945

• Edward S Miller, Bankrupting the Enemy: The U.S. Financial Siege of Japan Before Pearl Harbor

Greetings! There seems to be something of an interest in prewar Japan and its expansionist ambitions on AH, and that is something I wholeheartedly endorse. This response will deal with the part of OP's question about the Greater East Asia Co-Prosperity Sphere (or Dai Tōa Kyōeiken), and the origins of its ideological context in prewar Japan. It shall also focus on the wartime reality of the Co-Prosperity Sphere, though I shall leave the more in-depth analysis of Japan's wartime occupation policies and its expansionist aims to u/Lubyak, whose expertise on the matter is far greater than mine. As further AH reading of sorts, I highly recommend that you check out this comment from u/DanKensington which contains links to highly relevant posts regarding Japan's plans for war in the first place. With those preambulatory details out of the way, let us begin.

The Showa and Asia

"It is my belief that Heaven has chosen Japan as the champion of the East."

- Right wing philosopher and writer Shūmei Ōkawa, writing in the 1920s on Japan's relations to Asia

The quote above is one of the more iconic and highly-cited bits of primary evidence regarding the rise of anti-western sentiments within Japan in the Taisho democracy of the 1920s and the Showa era of the 1930s, which coincided with Japan's descent into the "Dark Valley" of ultranationalism and militarism. After continued "betrayals" and rejections by the western powers in the immediate postwar era, Japanese politicians and right-wing intellectuals began to see the west as a scourge on Asia, with its colonial influence in the region as proof of Western arrogance. Alongside Okawa, chief among these intellectuals was Kita Ikki, whose 1923 publication Nihon Kaizō Hōan Taikō (An Outline Plan for the Reorganization of Japan) called for the people and military to take action and secure Japan’s position as the liberator of Asia. Here’s an excerpt from that hallmark work laying out Japan’s “burden”:

“The nation has the right to initiate a war, not just for self-defence but also for the other nations and races who are suppressed by an unprincipled power.”

This rhetoric fitted nicely with another rising idea in Japan’s far-right groups, the idea of Pan-Asianism. Under this motivator, the Japanese nation would take it upon itself to lead the rest of Asia in seeking equality with the West, and breaking the colonial powers’ hold over the East. But do not be fooled that purveyors of this belief viewed Japan as equal to the rest of Asia. Ever since the Meiji Restoration, Pan-Asianists had viewed Japan’s role as a guide rather than an equal amongst the other Asian powers, believing that its modernization gave it such a right. Our historian companion Andrew Gordon on the matter:

“The Japanese press and political opponents of the government would put forth a rhetoric of Asia-wide (pan-Asian) solidarity as they beat the drums on behalf of causes such as Korean independence from China or Asian equality with the West. Their vision of Asian unity placed Japan in charge, as tutor and military hegemon.”

This idea caught on rather quickly during the reign of the Showa Emperor Hirohito, and in 1933 Prince Fuminaro Konoe (who would himself be Prime Minister at critical stages of Japan's wartime expansion in 1937 and 1941) set up a "brain trust" (essentially a think-tank) with the express purpose of drawing up plans for a New Order in East Asia. Many notable philosophers joined this brain trust and gave various public symposia dedicated to clarifying Japan's national polity (or kokutai) with regards to East Asia and beyond. Christopher Goto-Jones on the various sub-topics that this overarching ideological aim included:

"The issues at stake in these debates were serious: how could Japan overcome the cultural hegemony of modernity qua [in the capacity of] Westernization and somehow pass through this borrowed modernity into an authentic modernity of its own: how could (and should) Japan help other nations in Asia to do the same thing; and finally how could Japan build a regional order that encompassed other nations in Asia without that order being an empire?"

Keep in mind that all of this planning was, up until about 1942, very much an abstract bit of policy which did not contain any clearly-defined boundaries or methodology. The general rhetoric of "Asia for the Asians" was adopted by the Japanese in their ideological motivators for war, There was no concrete plan for how Asia would be "liberated" or "modernized" under Japan's tutelage, and even less of an idea as to how Japan would go about fostering the cooperation of the former colonies of European empires. Even within the intellectual and government circles, there was no clear definition on just how far the East Asia Co-Prosperity Sphere would extend. Some envisioned "Greater East Asia's population of a billion souls", with British India included within the sphere, and others even included the British dominions of New Zealand and Australia as members of the sphere.

As Japan moved towards war in Southeast Asia in the late 1930s however, Tokyo began to draw up general guidelines for the future of Asia's relation to Japan. Here we might observe two critical "areas" of Japanese presence. The first such area was Northeast Asia, which included Korea (already a Japanese vassal state "puppet" since 1910), Manchuria, and the newly-conquered regions of China. This area was to serve as an "integrated industrial complex", where the local resources and labour could be exploited by the Japanese to serve their interests and national needs. By contrast, Southeast Asia was to liberated from Western colonial control, and given independence. These territories would in turn, provide Japan with the resources that her economy required, and the markets for exports which would assure continued "collective prosperity" in the East Asia region. As a primary source on these general policy outlines, consider this statement delivered by then Foreign Minister Yōsuke Matsuoka on October 5th, 1940 to the United States (following the signing of the Tripartite Pact with Germany and Italy):

"The construction of a new order in East Asia means the construction of a new order (sic) under which Japan establishes the relationship of common existence and mutual prosperity with the peoples of each and every land in Greater East Asia, that is East Asia including the South Seas. In a position of equality with every other country, Japan may freely carry on enterprises, trade, and emigration to each and every land in Greater East Asia, and thereby be enabled to solve its population problem."

[bolded text for the purposes of this response]

Of course, pre-war planning is one thing. Wartime execution is another. In the next part of this response, we shall turn to the reality of establishing the Greater East Asia Co-Prosperity Sphere, and how the Pan-Asianism ideals of the Showa era translated poorly into Japan's wartime occupation reality.

Part 1 of 2