If you want to understand the intensifying showdown between the United States and Iran, consider the headline in The Washington Post on the threat of rapid nuclear proliferation: "Many Nations Ready to Break into Nuclear Club."

It highlights one of the dangers cited by those who favor military action against Iran. President Barack Obama says that if Iran gets the bomb, "other players in the region would feel it necessary to get their own nuclear weapons. So now you have the prospect of a nuclear arms race in the most volatile region in the world."

A plausible threat? It may sound that way. But it also sounded that way in 1981—when that Washington Post story ran.

Nuclear proliferation is always said to be on the verge of suddenly accelerating, and somehow it never does. In 1981, there were five declared nuclear powers—the U.S., the Soviet Union, China, Britain and France—as well as Israel, which was (and is) undeclared.

And today? The number of members added since then is not 15 but three: India, Pakistan and North Korea. Most of the other countries on the list of likely proliferators never came close—including Argentina, Chile, Morocco and Tunisia. Iraq tried and failed. Libya made an effort and then chose to give up.

The peril was greatly overblown. It probably is again. But our leaders are not about to let mere history debunk the apocalyptic scenarios. They are committed to a policy based on fear rather than experience.

The United States keeps trying to force Iran to abandon its suspected efforts to build a nuclear arsenal, and so far it has been rebuffed. Both Obama and Mitt Romney have said they would use force rather than let Iran acquire nukes. Chances are good that whoever wins in November, we will be at war with Tehran sometime in the next four years.

But there is no reason to think Iran would ever use such weapons, and there is little reason to think it would spur other countries to get them. If all it takes to unleash regional proliferation is one fearsome state with nukes, the Middle East would have gone through it already—since Israel has had them for decades.

Why would governments in the region respond differently to Iran? Many of them are allied with the U.S.—which means Iran can't attack or threaten them without fear of overwhelming retaliation. Turkey, as a member of NATO, enjoys a formal defense guarantee from Washington. The U.S. might offer similar assurances to Saudi Arabia, Egypt and other nervous neighbors.

One way or another, they would probably find they can manage fine. Iran is no scarier than Mao's China was in 1964, when it detonated its first atomic device. Writes Francis Gavin, a professor at the Lyndon B. Johnson School of Public Affairs at the University of Texas at Austin, "It was predicted that India, Indonesia and Japan might follow."

At the time, he noted in a 2009 article in International Security, "A U.S. government document identified 'at least 11 nations (India, Japan, Israel, Sweden, West Germany, Italy, Canada, Czechoslovakia, East Germany, Rumania and Yugoslavia)' with the capacity to go nuclear, a number that would soon 'grow substantially' to include 'South Africa, the United Arab Republic, Spain, Brazil and Mexico.'" Mexico?

In recent decades, some countries have actually given up their nukes—including Ukraine (which inherited them from the Soviet Union) and South Africa. Others, like Brazil and Sweden, have scrapped their weapons programs. After the Cold War, it was assumed the newly reunified Germany would want to assert its new status by joining the nuclear club. It has yet to exhibit a glimmer of interest.

A nuclear Iran would soon learn something previous nuclear powers already know: These weapons are not much use except to deter nuclear attack. What help have they been for the U.S. in Iraq or Afghanistan?

China invaded Vietnam in 1979 to force the enemy's withdrawal from Cambodia. The Vietnamese not only refused but sent the People's Liberation Army home with its tail between its legs. China regards Taiwan as part of its territory, but the island has remained functionally independent despite the threat of nuclear coercion.

If Iran does get nukes, its neighbors that have survived without them will find that nothing much has changed. Nuclear proliferation is the danger that lurks just over the horizon, and that's where it is likely to stay.

Steve Chapman blogs daily at newsblogs.chicagotribune.com/steve_chapman.