Racial quality is related to the degree of selection for greatness. If a tribe does not tolerate the harshest forge at the bottom of Hell it inevitably ends up subhuman compared to those who do tolerate it.
The modern white race in Europe is only great because ancient Aryans slaughtered a lot of natives in Europe and Europe is generally a harsh place. Those areas in Europe spared from the Aryan slaughters don't exactly do so well.
The same applies to selection in other races. For example Ashkenazis are smart because their environment was unbelievably harsh. It was the forges of cold weather and Christian intolerance that caused Ashkenazis to be so strong.
In general the easier the lives of the average members of a race were historically the worse the quality of the race is.