The Black Death (1347–1351) killed roughly a third of Europe's population. The economic consequence was paradoxical: real wages for surviving workers rose sharply because labor became scarce.
Peasants who had been bound to land and lord suddenly had bargaining power. Lords who needed their fields harvested had to offer better terms. The feudal system, already under stress, accelerated its decline.
This is an example of supply shock forcing institutional change. The plague didn't cause the end of feudalism — but it compressed a process that might have taken centuries into decades.