In India, the invading Indo-Aryans established a strict segregation
system to keep themselves separate from the local dark-skinned native
population. This system was so strict that it has lasted to this day and has
become known as the caste system. However, even the strictest
segregation (and Aryan laws prescribing punishments such as death for
miscegenation) did not prevent the majority population from eventually
swallowing up the ruling Aryans until the situation has been reached today
where only a very few high caste Brahmin Indians could still pass as
Europeans.

using Nubians, blacks, and Semites (or Arabs) to work on many of
their building projects or as general slaves.
At various stages the pharaohs also employed Nubian mercenaries,
and ultimately Nubia and Sudan were physically occupied and
incorporated into the Egyptian empire. Although the buildings of ancient
Egypt are very impressive—many having survived through to the presentday,
their construction was dependent on the Egyptian ability to organize
an unprecedented mass of human labor.
Under the direction of a scribe and architect, thousands of slaves and
regiments of soldiers labored for decades to create the great buildings,
using only levers, sleds, and massive ramps of earth.
It is impossible to think that such massive use of slave and foreign
labor would not have left some mark on the population of the land.
Interbreeding took place, and this, combined with the natural growth and
reproduction patterns of the slaves and laborers, meant that in a relatively
short time they comprised a significant section of the population.