Japan was not a nation blessed with many Natural Resources as was the U.S., and other enemies of that nation. In order to secure those additional raw materials, such as rubber, tin, and petroleum, among others, the war leaders decided that conquest of other nations was a solution, and began by attacking China, which in actuality was the (early) start of the war.
At the time, China was a virtual colony for many European nations, including England, France, Netherlands, and the US as well as Japan. Other colonies in Asia included Vietnam for France, Philippines for US, Indonesia for Netherlands, and so on. As the great powers competed for regional interests, Japan was quickly gaining ground from obtaining German concessions after participating on the allied side in WWI. The United States did not view Japan's intrusion into China as favorable to its own interests in the area, and thus economic frictions between US and Japan arose. At the time, Japan relied 80% of its resources, including oil, indispensable at the time, to the US. US began throttling its exports to Japan, and pressured its allies to do the same (such as the Netherlands and Mexico, which Japan sought to purchase oil as alternative sources). The friction reached its height when the US stopped all exports to Japan under the Export Control Act on July 31, 1940 after freezing all Japanese assets in the US, virtually cutting off all of Japan's access to resources. 4 months later, Japan decides to attack the United States on Pearl Harbor.
Japan was angry because after World War one they received little for aiding the allied countries. They decided that they could claim the land they needed if they helped the axis.
It was a chance to expand. Japan is after all, a very small country with one of the largest populations. Being small, it really needed recources and land. WWII gave it that chance.
They wanted to establish a vast empire for themselves in Asia and the pacific whose resources and people they could exploit for their own enrichment and empowerment.
Japan historically had many earthquakes and limited natural resources as the islands country. From early 15 century, from the European missionaries' outreach, they started corresponded to Europe and outer world out of their far-East territory.
Many Westerners know that German killed around 6 million Jews during World WarII, but many Westerners don't know Japanese killed over 12 millions Asians during World II.
I will be assuming this question is asking "why did Japan enter war with the United States", as the Pacific theater of war actually began in 1937 when a Japanese army stationed in Manchuria (which the Japanese state recognized as a separate, puppet country, Manchkuo) fought a "police action" in northern China (actually a plot by the Japanese army, without the government's consent, to invade northern China at the Marco Polo Bridge). Japan entered war with America because of one reason: oil. Japan, while a perfectly wonderful place, is not recourse rich, particularly in the oil department. The United States had been trying for several years to stop Japanese aggression in the east through sanctions and diplomacy, etc, to protect their own (and the UK, France, and the Netherlands) interests in the east (Indochina, the Philippines, Malaya, etc). The Japanese were mystified by this: the United States had never had a particular interest in the east (past the Philippines), and their sudden support of China came as a shock to the Japanese Government. In 1941, the United States stopped all oil exports to Japan, as the Japanese moved into French Indochina after the fall of France (this was a move to cut the Chinese defenders supplies that the Japanese military correctly deemed were flowing from Indochina). The Japanese absolutely depended on US oil; it may have been upwards of 85% of their entire supply! Japan, mired in a war with China that it couldn't seem to extricate itself from, and seeing the United States oil embargo as more proof that the West played by one rulebook and the east by another, lesser set of rules, were faced with a choice: back out of China and lose face (but regain oil), or continue the path of aggressive expansion that might provoke the United States into war (but possibly take territory with access to oil). They obviously chose the path of aggression, and prepared a devastating attack at the US pacific naval base Pearl Harbor in the hopes of crippling the United State's Pacific Fleet.
they ate potatotes
Domination of the East and the Pacific.
Economics, and access to raw materials.
* A totally dedicated and motivated Armed Forces. * A supportive homefront. * A powerful Navy.
the war was over
Germany wanted revenge after world war 1.
The Great Depression
Vladimir Lenin withdrew Russia from World War 1 by entering into the Treaty of Brest-Litovsk.
imperialism. militarism, and the alliance system.
Germany declared war on Poland. Poland didn't have a choice.
Japan had an Emporer.
racism, resouces, revenge
Maybe you haven't heard about the Japanese attack on Pearl Harbour on 7 December 1941.
The United States.