The United States had been pursuing an Open Door Policy in China - that is, they wanted to make sure the Chinese market was open to American products. The United States did not want China or portions of China to be controlled by other countires such as Japan, Britain or other European countries. Thus they objected to the Second Sino-Japanese War and the occupation of part of China by Japanese troops. In protest, the United States sent support to the Chinese Nationalist Government of Chiang Kai-shek, froze Japanese assets in the United States, and imposed an oil embargo on Japan.
In November of 1941 the Japanese government approved the for the attack on Pearl Harbor. At the same time, they made a last effort to arrive at a diplomatic solution of their differences with the United States (see entry for Hirohito). Ambassador Kichisaburo Nomura presented two proposals to the American government.
The first, proposal A, he presented on November 6, 1941. It proposed making a final settlement of the Sino-Japanese war with a partial withdrawal of Japanese troops. The United States had deciphered some of Japan's diplomatic codes, so they knew that there was a second, follow-up proposal in case proposal A failed. The United States government stalled and then rejected proposal A on November 14, 1941.
On November 20, Nomura presented proposal B, which proposed that Japan stop further military action in return for 1 million gallons of aviation fuel from the United States. The United States was about to make a counter offer to this plan which included a monthly supply of fuel for civilian use. However, President Roosevelt received a leak of Japan's war plan and news that Japanese troop ships were on their way to Indochina. He decided the Japanese were not being sincere in their negotiations and instructed Secretary of State Cordell Hull to drop the counter-proposal.
On November 26, 1941 Secretary Hull presented the Japanese ambassador with the 'Hull note', which as one of its conditions demanded the complete withdrawal of all Japanese troops from China. After a costly war to establish its interests there, Japan could not accept this. Japanese prime minister Hideki Tojo said to his cabinet, "this is an ultimatum."
The strike force which attacked Pearl Harbor set sail on the same day, November 26. It could have been recalled along the way, but no further diplomatic progress was made.