What!?
You need to go back to your books, dude. Japan wanted to be up there with the big boys of Europe. They initially wished to emulate the British in having a great empire and believed they had grown up and were ready to join the world - whatwith the industrialisation of the Meiji period and all.
However, the epic fail of Versailles (and Woodrow Wilson) caused the Japanese to feel highly slighted. The Washington Treaty was also handled stupidly and pissed the Japanese off even further.
Then, to seal the deal, the US told the Brits to not be so friendly with Japan - which the Brits duly did.
Isolated, slighted, and suffering from inferiority syndrome ("why don't the others treat us like equals!?"), they decided to go for their empire and expand into China. Everyone else was doing it, why not the Japanese?
I'm not saying if these actions are right or wrong, but the key is to understand why these actions came about in the first place. They didn't invade China for fun. China had resources, China has space, China had "inferior people" and China was a good chance to show the world that Japan was just as capable as the other great powers.
Then the US got heavy-handed with their deterrance policy and embargoed the crap out of Japan, which made expansion even more necessary for Japan and so on and so forth.
The roots of Japanese aggression in Asia could arguably have come from the fact that the rest of the great powers in Europe didn't give a crow's hoot to a "bunch of gooks" in the East who were trying their best to be considered equal on the world stage.