What were the problems caused by Japan because of Manchuria, especially between China and Japan, and what were the influences?

The tension between China and Japan has appeared for so many years. As a Chinese, I want to know more about what Japan did during 1930s and 1940s. I also want to understand what was actually going on between China and Japan, and how the problems affect people's life now. I checked up a few web sites, both in Chinese and English, so that the ideas wouldn't be too subjective or simplistic.
Japan's industry and military powers were developing very fast during the 1920s to 1930s, and its population was rapidly increasing as well. Japan's land was getting crowded. Manchuria had nearly 200,000 s…