But, then again, as another poster postulated, Abelas and his fellow Sentinels could be elite slave warriors similar to the Janissaries.
Describing the
yeniçeri as "slave warriors" is kinda like calling the US Marines "shipboard security officers". That was how they started out, but they became famous as something else entirely.
Only the first few generations of
yeniçeri were slaves; then, for a few centuries, they were conscripted from the Christian population of the Ottoman Empire as young boys. (Some people refer to this conscription, the
devşirme, as slave recruitment. This is definitionally incorrect: at no point were the men who served actually enslaved. They were abducted, conscripted, converted, and reeducated - all of which were Bad Things - but they were legally distinct from slaves.) By the late sixteenth century, even this conscription was dying out in favor of enlistment by Muslim subjects as a sort of militia. Christian conscription was finally outlawed in 1648, and the entire formation was abolished in 1826 in the Auspicious Incident. (Which was like a real-life version of the simultaneous assassination scene at the end of
The Godfather, except with armies.) So out of four and a half centuries of
yeniçeri, they were only "slave warriors" for a few decades.
Most of the time, people who are thinking of Muslim slave warriors mean the mamluks. Stratified warrior social groups - the word "caste" is often used, and although it is technically incorrect it is a decent simile for the situation - were common in the history of the Muslim world for a long time. The 'Abbasid khilafa is supposed to have begun the mamluk system, training units from Central Asian slaves as an alternative power base to the unreliable formations that predominated in the previous century (which led to military revolts such as the one that brought the 'Abbasid khalifas to power in the first place).
Unsurprisingly, the fact that mamluks were recruited from slaves did not make them significantly more loyal to specific rulers. The system persisted anyway,
faute de mieux. (I'm only being slightly facetious here.) Mamluks eventually became an entrenched group that could serve as a power base for ambitious military or political leaders, and after awhile those leaders began to come from the ranks of the mamluks themselves. Mamluks set up their own monarchies across the Muslim world: they were sultans of Egypt from 1250 to 1517, they ruled Iran and Central Asia in the twelfth century, they ruled northern India from Delhi in the thirteenth century, and mamluks in Iraq even achieved a measure of autonomy under the Ottoman Empire during the eighteenth century.