The main reasons why Japan attacked Pearl Harbor include:
1. Japanese expansionism: Japan had been engaged in a period of expansionism in the Asia-Pacific region in the 1930s, aiming to secure vital resources and establish its dominance in the region.
2. US sanctions and embargoes: In response to Japan's aggression, the United States had imposed various economic sanctions and embargoes, including an oil embargo, which threatened Japan's ability to fuel its military and economy.
3. US support for China: The United States was providing moral and material support to China, which was involved in a war against Japan since the late 1930s. Japan perceived this support as a threat to its interests and wanted to neutralize the US involvement in the region.
4. Preemptive strike: Japan hoped to cripple the US Pacific Fleet and its military strength in a preemptive strike, allowing them to establish dominance in the Pacific without US interference.
5. Miscalculation: Japanese misjudged the American response and believed that the US would not engage in a protracted war in the Pacific, hoping that a decisive blow would force a negotiated settlement in Japan's favor.