The Russo-Japanese War marked the first time that an Asian country beat a Western country. This was the first time that the U.S realized the true power of Japan.
While in League of Nations, the Japanese decided to invade Manchuria, and called in Manchukuo. The League of Nations reprimanded the Japanese, and the Japanes left the League of Nations, eventually signing the Tripartite Pact, becoming part of the Axes.
The Washington Naval Conference limited the tonnage of ships between the nations that won WWI. The ratios between the U.S, Britain, and Japan were 5:5:3, Japan being given the short end because the Americans were afraid of Japan's power. The Japanes didn't like to be given the short end of the stick, and this marked the beginning of strained relations between Japan and the U.S.
During the London Naval Conference, the ratio of tonnage of the Washington Naval Conference was changed from 10:10:6 to 10:10:7. The Japanese wanted to be equal to the U.S and France, but they didn't get their wish.
During the Marco Polo Bridge incident, the Japanese used a tiny discrepancy as an excuse to launch a full-scale assault on Japan. At this point the U.S began to realize the magnitude of the madness that was Japan.
The Japanese decided to bomb the naval fleet at Pearl Harbor to debilitate the U.S. and become able to invade Asia. They actually included Pearl Harbor as a series of coordinated attacks designed to debilitate the U.S and invade Asia.
The Japanese invaded Guam, a naval outpost of the U.S., for its strategic positioning, which could come in handy for WWII.