>all the roman civil wars
>even during the republic
>fuck logic

Simply because there is no "proper system of succession". Making it hereditary always causes problems - what if your son is an incompetent little shit? What if your children start killing each other, or even worse, you?

If you have some sort of council like the Kurultai, that also brings forth many problems, like when the Mongol leaders had to return from their military expeditions halfway across the world just to play a part in it.

>>Literally 90% of the wars and troubles of history are caused by unclear solutions of succession.

I'd say the vast majority of war is waged over resources to be honest, various casus beli aside. Like people will look for any fucking excuse to fight each other, a succession crisis is just a formalized version of that.

Your sucessors might die before you
Your sucessors might plot to kill you/each other
You have to worry about political consequences when designating successors

And in the end it might turn out that you picked someone shitty anyway.

>>1104991
Nothing better than having the feeling of leaving caos behind

>>1105002
This is the truth. There's no real winning. The best case scenario is to train your successor years in advance of when they would feasibly succeed you but that can go wrong as a result of various factors, such as them randomly dying for some reason.

>>1105002
Nerva figured put into practice a workable system, though it failed as soon as an emperor had a son to succeed him