The main events that led to the Japanese attack on Pearl Harbor were actions that Japan took in pursuit of an empire in Asia and the Pacific.  Added to this was the United States’ reaction to Japan’s actions.  The combination of Japanese actions and US reaction led to the attack.

In the time after WWI, Japan wanted to expand its empire in its general region of the world.  It wanted to be a major power with a large empire just like major European countries and the US.  Japan started by closing off foreign access to its League of Nations mandate in Micronesia.  This made the US worry that Japan was fortifying the islands and could use them to cut off American access to the Philippines (then a US territory) and the rest of Asia.  Later, Japan invaded Manchuria and left the League of Nations when that organization ordered it to evacuate its new territory.  After that, Japan invaded China.  These invasions happened in the 1930s.

Finally, Japan occupied French Indochina in July of 1941.  France had been defeated by Germany, which was Japan’s ally.  Therefore, France could not really resist Japan’s occupation of Indochina.  However, the Japanese occupation worried the US greatly.  In response, the US cut off supplies of oil and scrap iron to Japan.  This led to the attack on Pearl Harbor.

What Japanese actions led to the attack on Pearl Harbor?

In general, the Japanese actions that led to the attack on Pearl Harbor (other than the actual planning and carrying out of the attack) were actions that showed that Japan was trying to take an empire for itself in Asia and the Pacific.

These actions started after WWI.  Japan took islands (Micronesia) that had belonged to Germany and essentially made them part of its empire.  Japan was not supposed to be doing this, and its actions worried the US to some degree.  Later, Japan started to invade the Chinese mainland.  Japan first occupied Manchuria, ignoring the League of Nations when that body tried to tell it to leave Manchuria.  Then Japan invaded China.  Both of these actions worried the US still more because the US felt that a large and powerful Japan would be a danger to US interests. 

The Japanese action that led fairly directly to the Pearl Harbor attack came in July of 1941.  In that month, Japan occupied French Indochina, mostly what is now Vietnam.  The US felt that this was the last straw and that Japanese expansionism needed to be halted.  It cut off sales of oil and scrap iron to Japan.  This led Japan to attack Pearl Harbor.

What actions by the US led to the attack on Pearl Harbor?

The US actions that, arguably, led to the Japanese attack on Pearl Harbor were actions that seemed to be hemming the Japanese in and preventing them from becoming the major imperial power that they wanted to be.  We must note that this is not to say that the Japanese attack was justified.  Instead, we are saying here that there were American actions that helped cause the Japanese to attack Pearl Harbor.

The main American action came in July of 1941 after Japan had occupied what was then called French Indochina (Vietnam and surrounding areas).  America did not want Japan to do this because the US did not feel that the idea of a large Japanese empire was in its interests.  Therefore, the US demanded that Japan withdraw from Indochina.  It also froze Japanese assets in the United States.  More importantly, it stopped selling Japan scrap iron and oil.  This meant that the US was cutting off Japan’s major supply of fuel.

With this US action, Japan had only about two years’ worth of fuel for its military.  Japan felt that it needed to go to war soon so that it could capture an empire from which it could get the resources it needed.  If it waited too long, it would no longer have the fuel it needed to fight.  Therefore, the Japanese attacked Pearl Harbor.