The United States attempted to restrain Japanese aggression through trade sanctions
In the late 1930s, Japan relied on trade with the United States to operate its economy. Over 70% of Japanese imports of scrapped steel and iron came from the United States, as well as over 90% of its copper, and more than 80% of its oil. As their aggression in Asia continued, Roosevelt squeezed its economic lifelines, gradually cutting off most of the trade between the nations. Rather than curtailing Japanese aggression, FDR’s actions led the Japanese to further their own expansion. In 1940, following the Japanese move into the French colonies of Indochina, FDR curtailed shipments of scrap metals and aviation fuels to Japan via an embargo. The United States, which then controlled the Panama Canal, closed the waterway to all Japanese ships. All the while American diplomats continued to negotiate a peaceful solution with the Japanese.
Japan responded to the closure of the canal by occupying southern Indochina, placing their troops in a position to directly threaten British interests in Burma and Singapore. It also exhibited a threat against the oil-rich Dutch East Indies. FDR, in turn, finally cut off oil exports to Japan and froze their assets in the United States. For Japan, the oil embargo made war with the United States inevitable. Though they had been rehearsing a plan for a massive carrier raid on Pearl Harbor since early 1941, they still lacked one vital element in making war, the approval of the Emperor. Negotiations with the Americans continued, but Japan refused to withdraw from China, as well as changes to its alliance with Germany and Italy, as demanded by the United States. War warnings began to appear in the Pacific in October 1941.