Success in Ukraine will deter wars of aggression, prevent a global nuclear arms race and make World War 3 less likely.

Of course, the most powerful argument is the one I have not made yet: Helping Ukraine is the right thing to do. It is the American thing to do. As Reagan explained 40 years ago during his “Evil Empire” speech, the United States cannot remove itself “from the struggle between right and wrong and good and evil” because “America has kept alight the torch of freedom, not just for ourselves, but for millions of others around the world.” Those words ring as true today as they did in Reagan’s time. The war in Ukraine is a struggle between right and wrong and good and evil, and in that struggle, America must not remain neutral. Even this is a matter of self-interest. Since the end of the Cold War, democratic self-government has spread throughout the world. The dramatic expansion of human freedom has unleashed an unprecedented expansion of peace, stability and prosperity at home and abroad. But even those unpersuaded by Reagan’s call to oppose evil can still agree with him that the United States must pursue “peace through strength.” The “America First” isolationists of the 1930s hoped to avoid a repeat of the carnage of the First World War, which took some 20 million lives. Instead, their failure to resist Adolf Hitler’s rise invited the Second World War, which took 60 million lives. Allowing Hitler to seize the Sudetenland in Czechoslovakia did not appease the dictator nor deliver “peace for our time.” It only whetted Hitler’s appetite, and the appetites of other expansionist powers, for conquest. The same will be true if we allow Putin to seize Ukraine. The lesson of the 20th century is that putting “America First” requires us to project strength and deter our enemies from launching wars of aggression — so that U.S. troops to don’t have to fight and die in another global conflagration. The invasion in Ukraine was a failure of deterrence. Only by helping Ukraine win can we prevent further deterrence failures. If we help Ukraine prevail, we can rewrite the narrative of U.S. weakness; restore deterrence with China; strike a blow against the Sino-Russian alliance; decimate the Russian threat to Europe; increase burden-sharing with our allies; improve our military preparedness for other adversaries; stop a global nuclear arms race; dissuade other nuclear states from launching wars of aggression; and make World War III less likely.