Witness Real Deterrence

Germany waged two wars of aggression in the last century. What stopped them from starting a third was resounding defeat followed by decades of humiliating occupation. Japan thought they could conquer Asia. What put paid to that notion was two atomic bombs. There are ways to halt the Hitlers-in-the-making, but they aren't pretty. The only thing uglier would be to let the aggressive despots in Russia, Red China, and Iran realize their goals.