OK, let's imagine that Japan, with some alterations going back as early as 1918, is facing societal stresses, internal disorder and possibly civil war to the point that the country is not paying for a great power fleet in the 1920s and 1930s and is not invading its neighbors at all. I am contriving the end result of no aggressive & threatening Japan in the 1930s and early 1940s. My view is that it is at least a bit more plausible to have Japan not show up as a revisionist, expansionist power because it is internally chaotic and rent by strife rather than the opposite scenario of being a coherent democracy and simply not choosing to compete navally and commit military aggression.
Paul Kennedy made alot of the "two-front" dilemma posed for the UK and USSR (and I would extrapolate France & the USA also) posed by simultaneous aggressiveness by Imperial Japan and the European Fascist powers.
If Japan is a not a significant military-naval threat, will the British, French or Soviets be more willing to oppose Mussolini or Hitler earlier? Might they (and perhaps the U.S.) seriously sanction Italy over the Ethiopia invasion? Might they oppose the Germans and Italians in Spain with greater vigor. Or, if all else fails, might they decide they are not putting up with Hitler's crap when he starts claiming Czechoslovakia and will resist him by force?
Or, will all the powers follow the same appeasement and nonaggression pact policies pursued in OTL until the Germans and Italians bring war to Poland, and then to their own homelands?