Due to overpopulation from 1300 BC local peasants had to seek the employment as mercenaries in neighboring countries.
Later this practise was replaced by mamluk and janissarian systems. What started as a quest of middle eastern pedophiles to find young and beutiful white boys for sexual pleasures turned into primeral source of military recruitment in the middle east - young boys where kidnapped, and on a rare occasion sold by their parents.
From them the most wild and strong ones where selected to become elite fighters - mamluks. At first the percentage of caucasian per se was relatively small, and most of mamluks where actually kipchaqs - turkish tribe, pushed away by mongolians. Most of mamluks at Ain-Jalat where Kipchaqs. The mongolian army opposing them consisted mostly of georgian and armenian mercenaries.
But soon the situation changed and most of the newly acquired slaves where circassians and georgians (mostly western georgians - megrelians). They never mixed with the local population, maintained their identity, language, and served in squads with people of the same nationality. They often maintained their native religions - till XVII century paganism or christianity, despite being converted into islam.
Overly nationalistic but detailed review can be found here:
http://www.kartuli.com/site/modules....article&sid=74
Enclosed is a portrait of a georgian mameluk in his uniform (short sleeve tunic) and Napoleon's bodyguard armenian mamluk Rustam.
Also see:
http://users.panola.com/AAGHS/manluk.html
http://www.napoleon-series.org/milit...mameluks1.html