The War of the Spanish Succession
When the last Spanish Habsburg king died childless, the great powers of Europe went to war for thirteen years over who would inherit his vast empire, terrified of any one dynasty growing too strong. The peace that ended it deliberately balanced power among states — an early attempt to engineer a stable international order. Even in an age of settled monarchies, an empty throne remained a loaded weapon: the succession crisis as the era's most reliable trigger for general war.
The orderly transfer of power fails because no rule or claimant is accepted as legitimate.