If you have seen the film, there are a few things I have to clear up about some of the propaganda I used.
Japan's Nationally owned train in Manchuria, China, was not attacked by Chinese troops. It was attacked by their own troops, made to look like the Chinese had done it. They lied about it to the League of Nations so they could invade Manchuria on "justified reasons". They did setup a government for Manchuria, but it was a puppet government, which they had full control over.
Once Japan officially left the League of Nations, they held a military exercise on the border of China. In the past, they would notify China of these exercises, but on this one night, they hoped to have "an accident" and get a few Chinese troops to fire upon them. It worked. Despite the pleas from China to seize fire, Japan did not. Japan's reason for a full invasion had come. With massive amounts of troops already on the Mainland in Manchuria, it was an easy invasion.
All of the other information I used was true. I hope to clear that up before you all start to think Japan was too innocent.
Japan was ruthless, yet were not much different than the rest of the world, when it came to acquiring land. They just happened to attack a L.N. memeber. The U.S. Britain, Denmark, France and other nations had owned most of South east Asia. Japan felt the need to quickly grab the rest before it was too late. Korea was not enough and so the northern part of China was a good place to start. Once they had Manchuria (approx the size of Texas), they wanted China, a country weak and lawless, sought after by many world powers at the time. You may find the situation with Russia and Georgia to be very similiar.
For more information about why Japan went to War, I'd recommend you start reading some books!
here's a map of what SE Asia looked like in ~1930
A map of Burma