The Japanese air attack on Pearl Harbor (on the Hawaiian island of Oahu), December 7, 1941, was the climax of a decade of rising tension between Japan and the United States. Throughout the 1930s, Japan had been steadily encroaching on China. The United States had been trying to control Japan's development. Since America supplied more than half of Japan's iron, steel, and oil, Japan was hesitant to push the United States too far. It was also focusing on getting control of its own sources of raw materials.
On September 27, 1940, Japan joined the Triple Alliance with Italy and Germany and began to expand into northern Indochina. The United States,