My understanding is that in the 30's, two of the larger factions in the Imperial Japanese military opposed each other as to whether they should strike north at the Soviet Union, or south towards the Americans and Europeans. On the surface, the invasion of China in 1937 doesn't seem to further either of these goals; it's a massive drain on manpower against a second string power, without much in the way of strategic resources. What did the Japanese responsible for the invasion intend?
You might be interested in a past post on this topic:
Why did Japan invade China even after they took Manchuria?
^(21 Feb 2014 | 4 comments)
^(/u/ScipioAsina describes the economic and military pressures that contributed to the start of the Second Sino-Japanese War.)
/u/ParkSungJun might also be able to contribute to this topic.
You can ask followup questions by posting your questions in the comments with experts tagged to direct questions to them.
I'm a bit fuzzy on details by now, but I remember that the leadership and the junior officer ranks of the Kwantung Army ( 關東軍) of the IJM was aggressively in favor of military expansion into more central parts of China, especially after the Japanese takeover of Manchuria. I believe that a big part of the rest of IJM was heavily opposed to the Kwantung Army's intentions and the Kwantung Army as an organization, which was by far the (unintentionally for the central command) most autonomous section of the IJM-- that is, the central command was steadily losing its grip on the Kwantung Army leadership as the gulfs between different factions of the IJM deepened. I may be wrong on this count, but I think the Japanese invasion of China began partly as the accidental result of power struggle within the IJM.
It's been a while since I read on this subject so I may be wrong or giving a less than true impression of what the historical record shows.
I talk about this a bit here.