In 1991, of course, the Soviet Union dissolved. Ukraine, having avoided absorption into Russia thanks to Lenin, became independent. But the new nation encompassed as much land as it did thanks to Stalin.

When it was first formed, Soviet Ukraine had no natural border in the east with Soviet Russia. The demarcation disappointed all sides — and it is the site of today’s separatist rebellion. In the west, as a result of his 1939 pact with Hitler, Stalin seized eastern Poland and joined it to Ukraine. The city today known as Lviv was then a largely Polish- and Yiddish-speaking community, surrounded by a Ukrainian-speaking countryside; under Stalin and his successors the city would become predominantly Ukrainian-speaking — and the center of western Ukrainian nationalism.

With the defeat of Nazi Germany in 1945, Stalin annexed Transcarpathia, formerly part of Czechoslovakia, and now the southwest corner of Ukraine. Finally, Crimea, at the time a predominantly ethnic Russian territory, was transferred to Ukraine from Russia in a decision taken under Stalin but implemented only after he had died, in 1954, on the 300th anniversary of the Cossack request for imperial Russia’s protection against the Polish-Lithuanian commonwealth.

Except for Crimea, today’s nationalist Ukraine is a bequeathal of Stalin. It’s true that he executed countless officials of Ukrainian (and every other) ethnicity. But as the Soviet state expanded, he promoted still more Ukrainians to take their places. Even when he belatedly made study of Russian language a requirement in all Soviet schools, he did not discontinue instruction in national vernacular languages.

Of course, in helping to enlarge and consolidate Soviet Ukraine, Stalin never imagined that the Soviet Union would someday disappear. And so Mr. Putin faces a formidable obstacle.

He is said by diplomats to have told President George W. Bush, at a NATO summit meeting in Bucharest, Romania, in 2008 that “Ukraine is not even a state.” And in claiming territory from Ukraine, Mr. Putin has cited Catherine the Great’s Black Sea conquests and creation of “New Russia” in the late 18th century. But Mr. Putin cannot escape more recent history.

Russia’s annexation of Crimea has rendered Ukraine even more ethnically Ukrainian, and helped elect Ukraine’s first ever pro-European parliamentary majority. One does not have to take sides over the human tragedy unfolding in eastern Ukraine to grasp that, whether Mr. Putin does or does not have clear strategic goals, he cannot wipe out the fruits of the Soviet period.

Mr. Putin cannot simply swallow Ukraine — it is no longer “New Russia.” And unlike Stalin — indeed, because of Stalin, and because of his regime’s own behavior — Mr. Putin cannot entice Ukraine back into a new “Eurasian” union with Russia either. Ukrainians have little affection for Stalin’s dictatorship, but their struggle for statehood owes much to his legacy — a legacy that, for different reasons, neither they nor Mr. Putin like to think about.