A few years ago I ran a simulation game for a European military command. At the start, I gave the premise of the exercise as being that Iran had just obtained nuclear weapons. Then I asked the US "leader" how his country would respond. He explained that he would first consult with America's European allies. So I turned to the European "leader" and inquired what the European Union would do. Regardless of his personal opinion, he played his role accurately: "Nothing at all," he said. In a real sense, that's the point. As unwilling as anyone is to act seriously now to stop Iran's drive for nuclear weapons - unless you define UN sanctions that merely interfere with the travel plans or bank accounts of the handful of people running the program as serious - they will do even less when it is too late. And what will happen when it is too late? This is not a matter just of Iran possibly firing nuclear-tipped missiles at Israel, or more extreme officials handing such weapons to terrorists. These are extremely dangerous outcomes that might or might not happen. What should be more compelling is what would definitely take place: a gigantic shift in the regional balance of power against Western interests, and toward violence and instability. THE FIRST and most obvious situation would be a big boost for Iran's campaign to be the leading power in the Persian Gulf, or even in the whole region. For many countries and movements, having a patron with nuclear weapons will be incredibly attractive; for even more, having an enemy in possession of them is too scary to resist. Overnight, Iran will become the most attractive sponsor of political subversion and terrorism in the region. Saudi Arabia will still have money - but all those oil fields could, in theory, disappear in a very bright flash if someone in Teheran decided they should. Is this going to happen? Unlikely. But could the Saudis take that risk by angering Iran? The same applies to all the other small Persian Gulf Arab states. And if Iran has influence in Iraq now, what would it be like if Teheran had nukes? There are questions every Arab state would have to ask itself: Can the US be depended on as a protector? Will America, credibly, be ready to use its own atomic bombs to counter those of Iran even if it involves killing large numbers of people and getting involved in a terrible, bloody war? The point is that it is not the use of nuclear weapons but a credible willingness to use them - enough to convince rather extremist Iranian leaders - that brings strategic credibility. If you are a Saudi, Kuwaiti or Emirati, what would be your choice: to feel secure with an American promise of help, or to be safe by yielding to Iranian threats? Suppose, then, that Iran tells Bahrain not to house a US base, or Iraq to kick out American forces, or the Saudis to set an oil price to Iran's liking. Aren't the Gulf Arabs going to yield to their demand? Clear hints are just as effective as rude threats. The nastier the one who possesses the weapon, the more persuasive the warning. Then there is the equation's other side. Consider that you are a revolutionary opposition group, Islamist or otherwise, looking for a backer. For such needs, there was Egypt in the 1950s and 1960s, Syria in the 1960s and 1970s, and Iraq in the 1980s and 1990s. In the 21st century, however, no one can compete with Iran, as Hizbullah and Hamas have already decided. THERE WILL also be long lines in front of the recruiting counters of radical and terrorist groups. They might be wrong in expecting that Iran will provide their road to victory, but that will not stop them from staging large numbers of ever more daring attacks, convinced that Teheran's superior form of TNT will protect them. Tens of thousands of people will die as a result of their enthusiasm for the cause. And a lot of them might be in Europe. Do you think that anyone will make peace in the Arab-Israeli conflict if they assume - no matter how wrong they turn out to be - that Israel is going to be either erased by Iran's nuclear weapons, or intimidated into massive unilateral concessions? Do you believe the West will dare act effectively on any regional crisis in the face of Iranian opposition? Will Turkey protest firmly about Iranian involvement in Kurdish or Islamist subversion at home? This is only the beginning of the problems arising from Iranian possession of nuclear weapons: a bolder, extremist Iran; coercion of the local, relatively more moderate states; a boost for terrorist and revolutionary groups with an upsurge of violence, and intimidation of the West. And that's the optimistic scenario, without anyone actually using weapons of mass destruction. Keep this in mind as the crisis unfolds. The writer is director of the Global Research in International Affairs Center of the Interdisciplinary Center (IDC) in Herzliya, research director of the IDC's Lauder School, editor of Turkish Studies, and deputy director of the BESA Center for Strategic Studies.