Japan had a long history of wanting to expand its influence to gain access to materials, and in 1937 that desire led to the Second Sino-Japanese War, which was started with the Japanese invasion of China. The official start was considered the Marco Polo Bridge Incident, where the first shots of the war were fired.
Japan bragged that they could conquer all of China in three months. They began in Shanghai, and they expected an easy victory. However, China put up a good fight, and 92,000 Japanese died (283,000 Chinese died, but it was still a good resistance). Their resistance lasted three months, and was a good fight.
In December 1937, the Japanese Imperial Army invaded China's capital city of Nanking and killed 300,000 of 600,000 civilians and soldiers living in the city. They raped from 20,000 to 80,000 women, from ages 8 to 70, along with pregnant women. Overall, it was a terrible atrocity and was regarded as one of the worst atrocities in World War II.