Charles IV of France
When a monarch dies without a clear successor, a succession crisis often ensues, frequently resulting in a war of succession. For example, when King Charles IV of France died, the Hundred Years War erupted between Charles' cousin, Philip VI of France, and Charles' nephew, Edward III of England, to determine who would succeed Charles as the King of France. Where the line of succession is clear, it has sometimes happened that a pretender with a weak or spurious claim but military or political power usurps the throne.