“He was the first in the ‘Modern era’, not the first in the majors.”
True.
Interestingly enough, the first black player in the modern era could well have been Larry Doby or Monte Irvin had it not been for World War II. But many of the most talented black ballplayers were still overseas (Doby serving as a sailor in the Pacific, and Irvin an Army engineer in Europe). Had Robinson not been discharged early, we could be celebrating “Larry Doby Day” today.
You are correct regarding the war. There is another side to being ‘the first’ and that was temperament, the ability to take the initial abuse. Certainly Dolby and Irvin got their share but Robinson proved he could take it.