President Vladimir Putin may struggle to hold on to power if the war in Ukraine forces Russia to abandon military aggression and accept a peace deal with Europe, former US Secretary of State Henry Kissinger said.

“I would like a Russia that recognizes that its relations to Europe have to be based on agreement and a kind of consensus and I believe that this war will, if it’s ended properly, may make it achievable,” Kissinger told Bloomberg’s Editor-in-Chief John Micklethwait in an interview. Asked whether Putin could survive in power if the war ended on those terms, Kissinger replied: “It’s improbable.”

The veteran diplomat said it’s important that Ukraine emerges from the war as a strong democracy, and preferable to avoid “the dissolution of Russia or the reduction of Russia to resentful impotence” that risked stoking new tensions. He described Putin as a “Dostoevsky-type figure beset by ambivalences and unfulfillable aspirations,” who was very capable of wielding power as a leader and used it “excessively” in relation to Ukraine.

The June 7 interview in New York was a retrospective on Kissinger’s life and career after he recently turned 100. You can see the full recording here.

Putin has frequently welcomed Kissinger to Russia during his near quarter-century rule in the Kremlin and said at a 2012 meeting that their relationship stretched back to the mid-1990s when he was deputy mayor of St. Petersburg. Kissinger said in his Bloomberg interview that Putin was both the inheritor of a traditional Russian outlook and also someone who grew up on the streets of Leningrad, now St. Petersburg, where more than half the population died of starvation during World War II and faced constant threat.

Putin “translated that into never wanting European military power to be in easy reach of St. Petersburg and major cities like Moscow,” and reacted “at the edge of irrationality” to its expansion, Kissinger said.

While the US and its allies were correct to resist Russia’s attack on Ukraine, it’s “increasingly important” that parties to the conflict consider how they want to end it through diplomacy, Kissinger said. There’s a risk that military relations between powers dominate geopolitical thinking and turn the war into a global conflict by drawing in countries like China, he added.

“Europe will become more stable, the world will become more stable when Russia accepts the fact that it cannot conquer Europe, but it has to remain part of Europe by some sort of consensus as other states do,” he said. “But at the moment Russia is so crushed that it sees it’s being a factor of international politics in other regions and becomes a subject for European competition among the various states.”