Explanation: In the early-mid Ottoman Empire, there was no formalized succession system. The Ottoman Sultan would simply leave the throne to the strongest to the kid who could get to Constantinople the quickest whomever could acquire the necessary support after his death.

This was in part because the Ottomans came from nomadic Turkic origins - one chieftain succeeded another based on who was thought best to lead, not on strictly rules-based or hereditary criteria. However, while that is workable in a geographically concentrated tribe where everyone at least knows someone who knows the candidates, it was less viable in a pre-modern empire ruling over a vast stretch of the world. As such, it was important that succession was quick and uncontested to keep the Empire together and avoid civil war. The solution?

... whichever brother managed to scrape up the necessary support would simply have all other competitors for the throne assassinated - by being strangled with silk, so as to emphasize that it was a noble death, not the petty death of criminals. This included all of their brothers. Most often the eldest brother, who had the most time to prepare, would be the one to succeed, so it would usually be all the younger brothers who would get strangled.

... considering that child-sized coffins became the norm, there is something to be said for even the hereditary rule of European monarchies of the period.

Eventually, the Ottomans themselves realized that having this happen every succession was kind of a vile thing, and opted instead to ultra-isolate all the non-successor brothers instead of killing them by the Late Ottoman Empire. Progress!

Of course, this led to the issue that, whenever one of them needed to be carted out to replace a Sultan who failed to have kids of his own, said isolated prince would often be socially stunted and mentally ill from being cooped up in a single house with limited visitation rights for the entirety of his life.