Why did rome go through so many rulers?

Hey there!
Rome did not have a good system of succession. Rulers were not chosen carefully and that lead to major problems throughout Rome. Almost all rulers of Rome were murdered by either in cold blood or by poison. The next ruler had the same fate. Almost every ruler survived for no more than 2 years. 

(If you think that my answer has helped you, please consider rating it and giving it a thanks. And also please consider carefully considering the brainliest answer which doesn't have to be mine.)

Thanks!  :D

The answer is ethnic groups.