LAST EDITED ON 02-02-13 AT 02:13 AM (EST)Rulers killing off rival challengers is as old as the Bible. Even with a ruler clearly naming a successor the danger was still very real. Part of the problem, of course, was waiting for the old guy to die, no transition of power.
The Ottoman Dynasty had a pretty fun very chaotic rule of succession for a couple of centuries, basically it was open warfare. How it worked was when a Sultan died every one of his sons who wanted the throne would be prepared with their followers to take it by force, the rivals would go to battle, when one son captured another son he would execute his brother (or half-brother), and when only one was left standing he would be Sultan. It only makes sense, the Sultan would never be safe otherwise.