The personalist dictatorship, or tyranny, installed in Russia contributed to the Russian invasion of Ukraine and how Russia has fought. Tyranny is belligerent because the institutional design imposes few constraints on a tyrant’s decisionmaking. Moreover, this regime type exacerbates the ruler’s personal beliefs and misconceptions. It has a distinct life cycle, with economic performance giving way to stagnation, which prompts diversionary wars. Finally, Ukraine was especially vulnerable to attack from a personalist dictatorship like Putin’s. But due to rampant corruption, lack of information verification, and the ruler’s penchant for micromanagement, tyrannies usually fight badly, which explains Russia’s strategic failures in the early months of the war.