Manchuria
After Japan became industrialized and World War I, Japan's population was booming and they were beginning to run out of space for everyone in their small country. They needed more room, so they looked for the perfect place where some of their population could go. They decided that they should send a portion of their population to Manchuria, which was a north eastern region in China. Manchuria was also very rich in natural resources, which is something that Japan greatly lacks. In order to be able to stay in Manchuria, first they needed to make friends with the Chinese. They sent troops over to help build railroads and highways for the Chinese in Manchuria. In fact, the Chinese didn't even really care that they were there because they were in the mist of their own civil war. But the troops soon got disconnected from the government back home, and began looking for an excuse to go to war with China in order gain land and take over in order to make themselves look stronger. The Japanese ended up setting a bomb in one of their own railroads and blamed China for sabotage. The Japanese declared war, but the Chinese didn't want to engage in another war on top of their civil war. As a result of this, the Chinese asked the United Nations to tell the Japanese to leave. The Japanese government agreed with the United Nations and told their troops to come back, but the military wouldn't listen. The troops launched into a full scale invasion and took over many of China's major ports. But, the Chinese were distracted with their civil war, so before they new it, the Japanese military had already taken over nearly all of the Chinese east coast. Finally, Stalin got China's attention and told them to start fighting back. This may seem like a nice gesture and that he was just looking out for China, but really he was probably just looking out for his own country because he didn't want Japan to get too powerful and take over him next. But, since Japan was industrialized and China was not, a lot of the Japanese weapons were a lot for advanced to China fighting back almost had no effect. Over the next few years, the Japanese troops bombed and massacred China many times, and there wasn't really anything that China could do. Finally, the war reached a stalemate, and the troops ended up withdrawing from China. The Japanese government also withdrew from the League of Nations because they were being criticized about what they had done to China. After this, the Japanese felt like they were better than many other countries because they had the power to almost take over China. They felt this way when they went to bomb Pearl Harbor in order to try and scare the United States into an alliance. This was one of the causes of the United States entering World War II and World War II probably wouldn't have been as bad as it was if Japan hadn't been constantly looking for someone to fight in order to prove themselves.