Pearl Harbor Conspiracy Theory

One of the conspiracy theories that rose around the events of Pearl Harbour was that the military section of the U.S and have foreknowledge of the attacks and didn’t do anything to prevent it, so Franklin D. Roosevelt could declare war on the Japanese and join WWII.
One of the most important parts of America's advance knowledge of Japan's intentions was the U.S government's success in cracking Japan's secret communication code called “Purple”. Japan used it to communicate to its government groups, including some in Washington and Hawaii. A group of talented Americans broke this code in the 1940’s and this, developed U.S intelligence on both the War and Navy departments in Japan and revealed Japan's political messages. All of these decoded
ultimatum had now been received): The ambassadors were told a rupture in negotiations was "inevitable," but that Japan's leaders "do not wish you to give the impression that negotiations are broken off."
• November 30th: Tokyo ordered its Berlin embassy to inform the Germans that "the breaking out of war may come quicker than anyone dreams."
• December 1st: The deadline was again moved ahead. "to prevent the United States from becoming unduly suspicious, we have been advising the press and others that ... the negotiations are continuing."
• December 1st-2nd: The Japanese embassies in non-Axis nations around the world were directed to dispose of their secret documents and all but one copy of their codes. (This was for a reason easy to fathom — when war breaks out, the diplomatic offices of a hostile state lose their immunity and are normally overtaken. One copy of code was retained so that final instructions could be received, after which the last code copy would be destroyed.)
On three different occasions since 1894, Japan had made surprise attacks coinciding with breaks in diplomatic relations. President Roosevelt was informed on this history. Describing Roosevelt's White House conference noted that "The President said the Japanese were notorious for making an attack without warning and stated that we might be attacked, say next Monday, for
It is not even known who originally translated the intercept. One thing, however, is certain: The message's significance could not have been lost on the translator.

To ensure a successful Japanese attack — one that would enrage America into joining the war — it was vital to keep Kimmel and Short out of the intelligence loop. However, Washington did far more than this to facilitate the Japanese assault.
On November 25th, approximately one hour after the Japanese attack force left port for Hawaii, the U.S. Navy issued an order forbidding U.S. and Allied shipping to travel via the North Pacific. All transpacific shipping was rerouted through the South Pacific. This order was even applied to Russian ships docked on the American west coast. The purpose is easy to fathom. If any commercial ship accidentally stumbled on the Japanese task force, it might alert Pearl Harbor. As Rear Admiral Richmond K. Turner, the Navy's War Plans officer in 1941, frankly stated: "We were prepared to divert traffic when we believed war was imminent. We sent the traffic down via the Torres Strait, so that the track of the Japanese task force would be clear of any