We have already said that intense heat enervated men’s strength and courage, and that in cold climates a certain strength of body and mind made men capable of extended, hard, great, and daring acts. We observe this not only from one nation to another, but also between different parts of a single country. The northern peoples of China are more courageous than those in the south  the peoples of southern Korea are not as courageous as those of the north. 
We should therefore not be surprised that the feebleness of peoples of warm climates has almost always made slaves of them, and the courage of peoples of cold climates has kept them free. That is an effect that derives from its natural cause.
It was also found to be true in America : the despotic empires of Mexico and Peru were near the equator, and almost all the small and free peoples were and still are nearer to the poles.