Great Britain, France and Netherlands were barely holding onto their colonies in Southeast Asia. Those areas contained much of the resources that Japan needed, so it was logical that they sent their fleet out to capture those areas.
The US did not think the Japanese could launch multiple campaigns at once. The US expected only one attack. The belief was that Japan was suffering. The prolonged war with China and the US embargo that started in 1940 which halted gasoline, tools and airplane equipment was taking its toll. The US thought that stopping oil shipments in July 1941 and moving the US fleet from San Diego to Pearl Harbor would reduce Japanese aggression.
Japan needed to secure new supplies for the empire and Southeast Asia was the nearest option available. The allied forces were well aware of the Japanese intentions. It was not a secret. What was a secret was their strategy for achieving those objectives. Going after the US fleet at Pearl Harbor was considered counterproductive unless the fleet could be disabled long enough for the Japanese to secure their island positions and supply routes. Once secured, they hoped that the US would negotiate for peace instead of taking additional heavy casualties and making the resource commitments that would be required to break the defensive line Japan created in that time.
The Japanese commanders knew there was great risk in “waking up” America’s industrial might and patriotic fervor with a direct attack. President Roosevelt was worried that the public would not respond to calls for help from allies or demand a full declaration of war, unless an attack took place on US soil. The Philippines, a US protectorate, was seen as too far away and not part of the US public’s “America First” policies. The US public, tired of the death and destruction of fighting on foreign soils during WWI, was against going to war at all – especially another foreign war. Even the famed aviator, Charles Lindbergh, was a leading advocate for the “America First” movement and felt the US should remain out of the wars in Europe and Asia. Indeed, the Japanese completely misread the American public’s sentiment when they made their move on that fateful day that will live in infamy.