During the 1940's America was one of the largest suppliers of raw materials such as oil for Japan. Since the U.S. did not like Japan's aggressive tactics, "an embargo was established by the United States" (Takaki 87). This basically meant the United States would use their right to stop supplying Japan with raw war materials.
Japan responded to the Embargo by bombing Pearl Harbor on December 7th, 1941
After the bombing of Pearl Harbor, the United States had the responsibility of finding a safe and cost effective plan for dealing with Japan. The plan of invading Japan was discussed, but after many debates, this plan would result in "Horrific American causalities" (Stoff 19). Operation downfall was planned, but it was estimated "that upwards of 31,000 U.S. casualties could be expected within the first thirty days" (Long 48). After Operation Downfall was concluded as a bad plan, funding for the Manhattan project was in full affect. "The top priority for President Truman was to end the war as quickly as possible with the fewest U.S. casualties" (Baker 72). The United States expressed their right to construct a new nuclear weapon.
Operation Downfall was the plan to invade Japan with ground troops.