With Japan interested in expanding to the whole of Asia, they moved to take Manchuria for the vast resources; launching a war between the two nations.
How dare you?!
We didn't do it.
Help Us! This is your job!
The League hears you and we will talk to Japan. We will help you.
You guys need to leave China alone.
China went to the league for help to no avail as the league had no real power, though they did open the Lytton committee. Besides, both France and Great Britain supported Japan regardless of their actions against China so long as they didn't touch their lands.
Yea... that's up to the military.
We're not stopping.
The lack of support from the League left China vulnerable for the taking, which Japan took full advantage of.
The League would turn their backs on China completely, waiting for the situation to simply cease and Japan would leave the League, continuing on their conquest.
Oh well. We tried really hard with that one, let's relax now.