We should, of course, avoid what the philosopher Henri Bergson called the illusions of retrospective determinism. History seldom moves in straight lines. After Mr. Putin’s rise to supreme power in the Russian state, starting when he became prime minister in 1999, he experimented with other models of relations with the West and the rest of the world. For some years, he tried modernization in cooperation with the West. He embraced membership in the Group of 8 — one of several inducements that the United States and Europe offered to help Russia down its inevitably difficult post-imperial path. President George W. Bush got Mr. Putin wrong when he “looked the man in the eye” in 2001, but it would be bad history to conclude that the Putin of 2001 was already secretly planning to take back Crimea and destabilize eastern Ukraine.

Although historians should explore those paths not taken, it is nonetheless fascinating to see how the essentials of Mr. Putin’s resentment-fueled protector state doctrine were already there in 1994 — even if they were not then buttressed by ideological quotations from Russian thinkers like Ivan Ilyin.

Once upon a time, there was the Brezhnev Doctrine, which justified as “fraternal help” such actions as the Soviet invasion of Czechoslovakia in 1968. Mikhail S. Gorbachev replaced it with the Sinatra Doctrine —You do it your way, as Gennadi I. Gerasimov, the Foreign Ministry spokesman, put it — toward Eastern Europe. Now we have the Putin Doctrine.

It is impossible to overstate the degree to which this is a threat not just to Russia’s Eastern European and Eurasian neighbors but to the whole post-1945 international order. Across the world, countries see men and women living in other countries whom they regard as in some sense “their people.” What if, as has happened in the past, Chinese minorities in Southeast Asian countries were to be the targets of discrimination and popular anger, and China (where, on a visit this spring, I heard admiration expressed for Mr. Putin’s actions) decided to take up the mother country’s burden, exercising its völkisch responsibility to protect?

TO make clear why such actions are totally unacceptable, and a grave threat to world peace, we also have to agree on the legitimate rights and responsibilities of a mother country. My British passport still carries the resonant old formula that Her Britannic Majesty’s Secretary of State “requests and requires” foreign powers to let me pass “without let or hindrance,” and if I got into a spot of local difficulty in, say, Transnistria, I would hope (though not necessarily trust) that he would very earnestly require it. More relevant, Poland has expressed concern for the position of Polish speakers in Lithuania. Hungary has handed out both passports and voting rights in national elections to citizens of neighboring countries whom it deems to be members of the Hungarian people. To pin down what is illegitimate, we have to explain more clearly what is legitimate.