I meant based on when "Western culture" (meaning: people in US) started solving it. But you're right, gender identity was issue long before people started taking it as one.
Hmmmm ... civilization started near the point where "black" and "white" people meet. But yes, the idea that enslaving people of "correct" (white) color is not normal appeared only later, before that any other nation was fair game.
Informal doesn't mean nonsense, although I see that the term "breed" is now preferred term - oh. You mean the concept of dividing humans to races based on skin color. Well, before the "improved travel technologies" (was it really technology? Didn't the travel expanded for political reasons, like fall of Constantinople?) it might had some relevancy, although not nearly as big as it was claimed to ... interesting how the race started to be issue only when it's relevancy started to decline ...
... and by "interesting" I mean "suspicious".
Basically, the concept of race was used as an explanation that then existing cultural lines are fixed and there is no point trying to make those other people part of our culture. And the fact that you can't extend culture as fast as the conquest was happening was taken as confirmation.
Now, after several centuries, it is apparent that "other races" can became part of our culture if we let them (and if they want to).