After the Marco Polo Bridge incident in 1937, Japan, really under the junta-like leadership of the IJA, declared war on China and invaded from their territories in Manchuria.
What followed was a 8 year long slog, with many key tactical victories over the Chinese forces but nothing decisive enough to win the war.
So from 1937 - 1941, what could the Japanese(IJA) have done differently to score a decisive victory in China and effectively knock them out?
What peace arrangement could be garnered, depending on your answer?
What would be the long term effects geo-politically, diplomatically?
The Japanese treated the Chinese very like Whites treated American Indians. We'll take this land, you go over there. Oh. That land has something valuable, we'll take it, too.
Except where white incursion onto Indian land was spearheaded by farmers and prospectors, Japanese incursions were spearheaded by junior army officers.
There IS no possible 'peace arrangement', unfortunately. Japanese policy was determined by junior army officers who totally ignored directions from Tokyo, and just did what they wanted.
Plus, even the central government in Tokyo was completely [censored].
The Chinese 'puppets' they did set up were not client states, but Japanese run states with a puppet figurehead. Slaves, not servants, if you will.
If you managed to fix Japanese policy so they could KEEP any agreement they made (possibly by stomping on the first 'policy by assassination' efforts, that they let people get away with, iOTL), then you don't have the invasion of China (aside from Manchuria) in the first place.