Why did Japan participate in World War 2 ?

 

     The causes of Japan Empire participated the World War 2

 

Need for resources, amoungst other things. For Japan, WWII was the climax of its gradual expansion in the West pacific region dating back to the late 1800s.
The attack against the US was because it regarded the US as hostile and figured it had better try and weaken it while it could (IIRC, US had been very vocaly against Japan's invasion of Mancuria, despite the US's own occupation of the Philipines), plus US controlled territories on the region offered rich pickings.
Agreements with Germany/Italy, a pragmatic arrangement of powers opposed to the status quo.

The Japanese were intent on creating their East Asia Greater Prosperity Sphere with themselves at the helm. The Japanese were incredibly militaristic, absolutely devoted to their Emperor. They were also racist to the degree that they thought their civilization was superior to all others and were willing to destroy the other civilizations in wartime.

The Japanese attacked China, French Indochina and many islands in the Pacific amongst other countries. Japan needed raw materials and items like rubber and oil. They wanted it because their islands are rather small, and not able to support the greatest nation like they believed themselves to be.

Like other nations such as Germany and Italy, Japan believed the League of Nations would only issue threats from a desk, not back them up in any way.

Japan had a lot to prove in their minds as well. The West had always looked at them as being backwards. Japan moved rapidly towards modernization near the end of the 19th century. In fact for fun, watch the Last Samurai to pick up on some of this.

Japan became quite a powerful entity by the early 20th century and defeated the Russian fleet in the Russo-Japanese War. While Japan got on the map, they still felt they were not viewed as equals in the eyes of the other Western nations. This will be part of the reason they go on their Imperial crusade, pride.

Japan attacked the US because we had effectively placed an economic embargo on them by freezing their assets. As well, they wanted to control the Pacific and believed that we needed to move out. The Phillipines and other islands were in our hands as a result of the Spanish-American War. Pearl Harbor was in fact the headquarters of our Pacific Navy. Had our aircraft carriers been in the harbor at the time, they may have dealt us a horrific blow that we might never have been able to recover from.

I hope this helps you in some way.