I just finished it. It goes up to the point where he tries to go to Europe to document black fighter pilots in the US air force fighting the Nazis. Back then, the US military was segregated by race. Blacks were in separate units, while all other races in the US (whites, Hispanics, Asians, etc) were all together....only blacks were segregated. The military didn't want him photographing the black air squadrons and making heros of blacks.
He got into photography almost by accident and quickly discovered the power of photography to document the repression of blacks and poor people.