Also, not all janissaries were trained as soldiers. The cream of the crop were rather taught to be scholars and administrators.
They eventually wound up dominating, dethroning and even killing Sultans who got in their way.
Or, or an even more ancient bit of ancient history consider the career of Daniel. Marched 500 miles to Babylon, perhaps after being neutered. Trained in the lore of his captors. A top bureaucrat whose career spanned several empires. The leaders can play their games of musical chairs, but the bureaucracy outlives them all!
Interestingly enough, the janissaries were single, if not celebate. Imperial service is not compatible with family formation. They finally overturned their soup kettles (traditional signal for a mutiny) one time too many, and were exterminated by an even newer military unit, modeled after the European pattern.