causes of Japanese attack on Pearl Harbour could be traced back to two years before when Poosevelt made policies for helping Britain against Germany. Attack on Pearl Harbour was what finally brought US to WWII> Ironically, Japans decision to attack the US was a direct result of Roosevlets efforts to help Bri in its war against Ger. Roosevlet introduced policies to discourage the Japanese from attacking the British empire. Roosevelt began putting economic pressure on Japan. Japan depeneded on US for many key materials. The Export Control Act, gave roosevelt the power to restrict the sale of strategic materials to other nations. Roosevelt blocked the sale of airplane fuel and scrap iron to Japan. Furious at US, Japanese signed an alliance with Germany and Italy, becoming member of the Axis. Later, American intelligence decoded Japanese communications that made it cleaer Japan was preparing to go to war against US. in Novemer, US commaders received a war warning at Pearl Harbour, but Hawaii was not mentioned as a target, so they were not suspicious. Japans surporise attack on December 7th, 1941, sank or damaged 21 ships of the US. Japan was now at war with US. Hitler believed time had come to declare war on US to protect Japan. Hitler underetimated the strength of the US. December 11th, Germany and Italy both declared war on US.