The Hundred Years War…
It went on for 116 years.
Been studying it for a few years now. Probably the most deadly war in human history per capita. Half of Europe perished during it. In 1348 the Black Prince brings the plague back across the channel with claims of great victory over an already infected population of France. Much rejoicing goes on until everyone is dead or burying the dead.
This is actually one of the main reasons for the end of the feudal system. An extreme shortage of labor that allowed most people to seek better opportunity under other knights and barons that. Sort of a demand your own contract thing that had to be bowed to otherwise fields rotted and nothing would get planted.