Pearl Harbour: what did Roosevelt know?

On December 1, six days before Pearl Harbour, Roosevelt had given the British ambassador a clear commitment of support in the event of war. Why did he do so?

After Admiral Nagumo's force set sail for Pearl Harbour on November 26, the American government seemed - or appeared to seem - totally unaware of the movement of ships. They knew that Japanese forces were heading from Indo-China towards Malaya and Thailand: then why were they oblivious to this movement? After all, America had been doing its best to crush the life out of the Japanese economy with sanctions.

Churchill knew about Nagumo's fleet, and must surely have passed on the message to Roosevelt. What did he hope to gain by deceiving the Americans? The destruction of the American Pacific fleet could hardly have helped Britain.

Therefore, either Churchill or Roosevelt was withholding information - the former from the Americans, the latter from the American people. Since the first hypothesis must be ruled out, the second must be retained.

Roosevelt deliberately allowed around 3,000 Americans to be murdered so he could take America into the war.

Sound familiar?