https://www.google.com/books/edition/The_Politics_of_Success...
> this book also shows that the development and spread of primogeniture - the eldest-son-taking-the-throne - mitigated the problem of succession in Europe in the period after AD 1000. The predictability and stability that followed from a clear hereditary principle outweighed the problems of incompetent and irrational rulers sometimes inheriting power. The data used in the book demonstrates that primogeniture reduced the risk of depositions and civil war following the inevitable deaths of leaders.