Why Did Japan Attack Pearl Harbor in 1941¿ ¦ Full Color Documentary The attack on Pearl Harbor in December 1941 forever changed the course of World War II. Japan did not make this decision lightly: behind this move was the urgent need to secure strategic resources, especially oil and raw materials, vital to sustaining its military expansion in Asia and the Pacific. The United States’ economic sanctions created immense pressure on Japan. These restrictions threatened the very survival of its war