WASHINGTON — For decades, the threat of nuclear conflict between the U.S. and the Soviet Union hung over humanity — and occasionally the superpowers edged toward the brink, as with the Cuban missile crisis .

But beginning in the 1970s, American and Soviet leaders started taking steps toward de-escalation, leading to a handful of critical treaties, including the 1987 Intermediate-range Nuclear Forces Treaty that eliminated an entire class of nuclear-capable missiles.

The pact was terminated in 2019 after the U.S. withdrew. On Tuesday, Russia announced it was ending self-imposed restrictions on the deployment of the missiles covered in the agreement.

That leaves just one nuclear arms pact between Moscow and Washington still standing: New START, which experts say is on the ropes and

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