Two nuclear-armed states on a collision course with no obvious exit ramp. An erratic Russian leader using apocalyptic language — “if you want us to all meet in hell, it’s up to you.” Showdowns at the United Nations, with each side accusing the other of essentially gambling with Armageddon.

For six decades, the Cuban missile crisis has been viewed as the defining confrontation of the modern age, the world’s closest brush with nuclear annihilation. The war in Ukraine presents perils of at least equal magnitude, particularly now that Vladimir Putin has backed himself into a corner by declaring large chunks of neighboring Ukraine as belonging to Russia “forever.”

As two countries proceed up an escalatory ladder, mistakes become increasingly likely — as the Cuban missile crisis made clear. In a conventional war, it is possible for political leaders to make significant mistakes and for the human race to survive, battered but intact. In a nuclear standoff, even a minor misunderstanding or miscommunication can have catastrophic consequences.

In October 1962, it was President John Kennedy who declared a naval blockade, or quarantine, of Cuba to prevent reinforcement of the Soviet military position on the island. This put the onus on his Kremlin counterpart, Nikita Khrushchev, to either accept the clearly signaled American condition for ending the crisis (a full withdrawal of Soviet missiles from Cuba) or risk nuclear war.

This time, the roles are reversed: Mr. Putin is seeking to enforce a red line by insisting he will use “all available means,” including his nuclear arsenal, to defend the newly, unilaterally expanded borders of Mother Russia. President Biden has promised to support Ukraine’s attempts to defend itself. It is unclear how Mr. Putin will react to his red line being ignored.

Even if we assume Mr. Putin is a rational actor who wishes to avoid nuclear annihilation, that is not necessarily reassuring. Contrary to popular belief, the biggest danger of nuclear war in October 1962 did not arise from the so-called eyeball-to-eyeball confrontation between Khrushchev and Kennedy but from their inability to control events that they themselves had set in motion.