Both the Marco Polo bridge incident and Khalkin Gol battle were not exactly planned events on the part of the IJA, and in both cases the IJA just rolled with what happened.
The Marco Polo Bridge incident which happened in July 7th 1937 saw Chiang Kai-shek escalating into a full war between China and Japan, which was something Chiang originally wanted to delay a few more years until he thought China was 'ready'. Soon after you have a swift Japanese invasion of most of Northern China and central China.
Khalkin Gol, on the other hand, was an accidental incursion of Japanese troops into Outer Mongolia in 1939 which was met with Soviet force. Unlike the Nationalist Chinese, the Soviets were well equipped and relatively well trained. The battle was a defeat for the IJA, which put their plans of invading the Soviet Union on hold.
But what if an accidental skirmish/battle between the Japan and the Soviets happened in 1937, and skirmish/battle happened between Japan and China happened in 1939?
Would the Soviets still win? Would the Japanese decide to invade the Soviet Union first in 1937? Or would a defeat cause the Japanese army to decide to modernise/be less aggressive?
And if Chiang Kaishek gets the two extra years he wanted how much better would the nationalists actually do? How much more assets does Chiang have to work with? Would the war still be a stalemate, or would the Nationalists manage to score a victory against Japan similar to the one the Soviets scored against Nazi Germany in OTL?
Thanks.