This is a broad and interesting question, and there are a couple of ways of approaching it. There's one popular approach which you often find, which is to focus on Japan's material needs: the argument goes that Japan is a resource-poor country, and the need for expansion to fuel its economy inevitably brought it into conflict with the other major pacific power, the US. This is a bit of a superficial answer, though, in that it leaves out the key question of what the historical actors of the time were actually thinking.

My interest is in the history of political thought, so I want to focus on this intellectual element, that is, what sort of thinking influenced Japanese policymakers in becoming antagonistic to America. This isn't intended as a comprehensive answer by any means, though.

Origins of Pan-Asianism

It's impossible to understand Japan in this period without a sense of its peculiarity in the global context. In 1905, with the successful conclusion of the Russo-Japanese War, Japan became the first major non-Western power to defeat a Western country. This secured for it recognition as the only non-Western (and non-white) great power, which in turn encouraged Japanese pride and a keen sense of this uniqueness.

This was articulated in political thought in the 1910s and 20s, when a section of Japanese intellectuals began to argue forcefully for the idea that Japan had a historical mission to bring to an end Western domination of the world. This wasn't an entirely new idea -- Japanese exceptionalism has a very long history. But the intellectuals of this period expressed it in novel ways in a current that became known as "Pan-Asianism", which supported the idea of Asian unity under Japan in a struggle for independence from the West. Now versions of Pan-Asianism had already developed in the 1880s and 90s -- in 1898, for instance, Konoe Atsumaro had argued that the "yellow race" would need to be united to defeat the white race -- but it was the victory over Russia and the events of World War I that galvanised it into an influential movement.

One of the most prominent of these intellectuals was Kita Ikki, who can serve as a good example. Kita had developed a synthesis of nationalism and socialism beginning in the 1900s but revised his ideas in light of the Russian Revolution and his disillusionment with Chinese republican ideas in the decade after the Xinhai Revolution in 1911. In 1919, in the aftermath of Versailles (and the American rejection of Japan's call for a racial equality clause), Kita wrote:

That the star flag of America presided over the meeting at the Versailles palace implicitly reveals that it was a dark night for the world. The Japanese rising sun flag, after defeating England, making India independent and China self-reliant will shed the light of Heaven on all the people of the world. ... It will only be then that the real awakening of the 700 million people of China and India begins. On the road to Heaven there is no peace without war.

(An Outline Plan for the Reorganization of Japan, 1919)

Kita became immensely influential among younger officers in the Japanese military, though he was ultimately executed for taking part in an attempted far-right coup called the February 26 incident in 1936.

Ishiwara Kanji and Manchuria

One of the leading lights in the turn to a concrete anti-American policy was Ishiwara Kanji, an army officer, strategist, and part-time religio-political philosopher, who was a lecturer in the Japanese army Staff College and then an influential figure in the Kwantung Army. Though Ishiwara later disagreed violently with the Japanese government's conduct of the war, and departed from policymaking circles thereafter, in the 20s and 30s he was a major factor in the adoption of anti-American military policy, and later a driving force behind the occupation of Manchuria. Arguably, he did more than any other single person to push Japan towards war with America.

Ishiwara was deeply influenced by Pan-Asianist currents of thinking, and similarly to people like Kita he adopted a generally hostile view of America from an early stage. Ishiwara studied abroad in Germany for a period, and one anecdote has him meeting an American military officer there who invited him to visit the US -- Ishiwara replied that he would, as commander of the Japanese occupation forces.

By mapping the military history of the world (see also -- diagrams adapted from Mark Peattie, Ishiwara Kanji and Japan's Confrontation with the West), and through the influence of his own apocalyptic brand of Nichiren Buddhism, in the 1920s Ishiwara came to believe that the world was accelerating towards what he called the Final War (最終戦争, saishū sensō) between the East and the West, represented by their hegemonic powers, Japan and the United States. He viewed it as an urgent necessity for Japan to direct its national policy towards preparing for this war.

In light of this, in his lectures at the army Staff College in 1927, Ishiwara argued that "... by following the principle that 'war can maintain war' (sensō ni yori sensō o yashinau), Japan should be able to build up a self-sufficient industrial power base on the Asian continent. From this invincible base Japan could then make preparations to fight the coming war of annihilation with the United States" (Peattie). Though a pan-Asianist who viewed Japan as fundamentally fighting for the interests of all Asians, Ishiwara saw the occupation of Manchuria in particular and the establishment of Japanese supremacy in Asia as a sine qua non for fighting America -- referring to Napoleon's Continental System as a model.

After 1928, when he became an officer in the Kwantung Army stationed in Manchuria, Ishiwara agitated for the army to seize control of the region, and along with a cabal of other officers he was able to execute this plan in 1931. The Manchurian incident locked the Japanese government onto a course of policy that it didn't necessarily desire, and was an essential part of pushing Japan towards war with America: this flagrant violation of international norms in the Pacific, which developed into a broader conflict with China, posed a serious challenge to the US as well. It was impossible for the Japanese government to pursue peace with America indefinitely without antagonising the military by relinquishing its gains on the Asian mainland.

(continued...)