This sounds very simmilar to the "War of the Roses" crisis that England has to deal with at the start of eu4. No clear heir leading to civil war, powerful neighbours to contend with etc. This is also something that can be avoided by a player able to get an heir in time, so I thing eu5 might borrow from this mechanc.
The saddest part of the war was that in the end after John VI Kantakouzenos had finally defeated the regency and claimed ultimate victory, he refused to consolidate his victory and whatever power that the Byzantine Empire had left by purging his enemies and declaring himself Emperor and he brought forth peace terms that could have been reached prior to the war if the Regency hadn't been so stupidly stubborn.
This directly led to a continuation of the civil war just a few years later and this time John VI Kantakouzenos was not so lucky and ended up deposed to Moria by the ones he had granted mercy to. It also led to the Ottoman's first victory and expansion of territory past the Bosporus.
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