If the phrase “missile gap” rings a bell, you probably remember one of the most frightening periods of the Cold War era: when the United States and Soviet Russia, 50 years ago this month, came perilously close to launching World War III.

Not that it would have been a long war. Considering the relatively new nuclear capabilities of both nations, the horrifying prospect of leveled cities, mass casualties and general chaos loomed as what became known as the Cuban missile crisis took place.

How that crisis unfolded in October 1962 was dictated largely by how World War II had ended. The U.S. had dropped atomic bombs on Hiroshima and Nagasaki, and suddenly conventional wars fought by armies in the field seemed obsolete. The fact that a nation’s leaders could lay waste to an enemy simply by pushing a button forever altered the way leaders could broker conflicts.

The result: proxy wars in global hot spots, such as Korea in the early 1950s, as the freedom-loving West sought to oppose communist expansion worldwide. So when Cuba, just 90 miles off the coast of Florida, became the seat of a communist government in 1959, it set off some serious alarm bells for the United States.

The U.S. attempted to unseat the Cuban government through covert operations such as the failed Bay of Pigs invasion in 1961. Then came news that shocked U.S. officials: the Soviet Union was helping the Cubans build secret bases for missiles capable of reaching the U.S. Every “duck and cover” exercise, every air-raid drill, seemed like the prelude to a horrifying reality.

Thus began the tensest stand-off in modern history, with President John Kennedy and Soviet Premier Nikita Khrushchev attempting to stare one another down. Kennedy ordered a blockade of Cuba to prevent any more offensive weapons from going in, and demanded that the missiles there be dismantled and removed. The world waited -- and prayed.

After several tense days, Khrushchev relented. His main condition: that the U.S. agree to never attempt to invade Cuba again. The world’s brush with nuclear annihilation had ended.

Or had it? Perhaps subsided would be more accurate. Because from then on, a situation known as Mutually Assured Destruction (MAD) prevailed between the two global superpowers.

The arms race continued. Missile silos were filled with enough nuclear warheads to bury both sides in rubble many times over. And neither side dared press that button -- a first strike would certainly bring enough retaliatory firepower to make the attempt completely foolhardy. Détente, or “containment,” became the order of the day.

That changed under President Reagan, who wisely stepped up the arms race enough to make it financially unsustainable for the Soviets. He also conceived of a missile defense that would shoot down any incoming Soviet missiles.

Funding for President Reagan’s dream continued after he left office, and the Cold War ended. Today we have the technological capability to protect ourselves from certain missiles fired at U.S. territory or allies. But the system isn’t as comprehensive as what we would need to ensure that the potential missile threat posed by Iran, for example, can be shot down.

In fact, President Obama has undercut missile defense since taking office. That has to change -- and soon. We need a shield that will intercept missiles during all three stages of flight. It’s especially important to pursue a space-based component, which would enable us to shoot down missiles earlier in their flight, when they’re moving more slowly.

50 years ago, the world stood on the brink, and lived to tell the tale. We can’t assume we’ll get lucky the next time. Let’s build the kind of missile defense that will make us impervious to threats, and keep World War III at bay.

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Ed Feulner is president of The Heritage Foundation (heritage.org)