Opinion | Putin Began His Unjust War One Year Ago. Here’s What Ukraine Needs Now.

The first reason, and the one that prompted an immediate response from the West, is the moral and ethical obligation of the world’s democracies to help a nation whose freedom is threatened by an authoritarian power. National self-determination has long been a guiding principle of American foreign policy. Various U.S. administrations have honored it imperfectly, as is the case with so many guiding principles. But it remains valuable in finding a way forward. In sending an armored column toward Kyiv and seeking to overthrow its government, Mr. Putin clearly violated that principle, and threatens to return Europe to the instability of previous eras, when nations frequently invaded each other and altered the continent’s borders by force.

Russians might argue that the United States is hardly the innocent in its global dealings, whether invading Iraq on false pretenses, or covertly working to overthrow governments in, among others, Chile and Nicaragua. Certainly, there is much to criticize and debate in America’s foreign policy during and since the Cold War. There are also those, notably the political scientist John Mearsheimer, who further argue that the United States provoked Mr. Putin by failing to respect Russia’s national interests and, at one point, pushing to bring Ukraine (and Georgia) into NATO.

The wisdom of incorporating former Soviet bloc countries into NATO remains a topic of considerable disagreement among historians, but it is important to remember that it was not NATO that rushed to expand. Rather, many countries that had suffered Moscow’s repressive and often brutal control urgently sought the protections of the Western alliance against what they anticipated and feared would be a resurgence of Russian ambitions. As for Ukraine, the prospect of joining NATO anytime soon had dissipated long before the Russian invasion.

It was Ukrainians who rose up in the “Orange Revolution” against elections rigged to produce a pro-Russian outcome in 2004, and Ukrainians who took to the streets again in 2014 over President Viktor Yanukovich’s last-minute decision not seek closer relations with the European Union. The danger Mr. Putin saw was not to Russia’s sphere of influence, but to his personal sphere of power; a democratic, pro-Western Ukraine threatened to spread ideas that would directly challenge his monopoly on power. It is no coincidence that Mr. Putin’s growing aggressiveness toward the West developed in tandem with his growing authoritarianism at home. As his regime grew ever more repressive, his need for foreign threats, real or concocted, increased proportionately, to justify tightening the screws on domestic opposition.

In the end, nothing the United States or its allies have done or have failed to do in the three decades since the collapse of the Soviet Union even remotely justifies Mr. Putin’s attempt to bend Ukraine to his will by brute force. He has to be stopped, and Ukraine has to be allowed to choose a democratic, independent future. That is what U.S. leaders should stress in justifying continued support.