The conventional wisdom is that if Iran acquired nuclear weapons capability that this will likely spark a region-wide nuclear arms race. But as my colleagues Brian Katulis and Peter Juul point out there are some reasons to doubt this is right:
But there is no real reason to assume that Iran’s neighbors will automatically build their own nuclear weapons for the same security reasons that drove the United States and the Soviet Union to do so during and after World War II. Israel, after all, has possessed nuclear weapons since the late 1960s, and none of its neighbors—all of whom were at war with Israel at the time it developed nuclear weapons—acquired their own bombs. [...]
Interestingly, there has been a test case over the last decade of the arms race model in Northeast Asia. North Korea’s withdrawal from the Nuclear Non-Proliferation Treaty in 2003 and subsequent nuclear tests in 2006 and 2009 have not set off a wave of proliferation in the region. Japan and South Korea, both technically capable of building nuclear weapons and having legitimate security concerns vis-à-vis North Korea, have not begun their own weapons programs. Their failure to do so calls into question the accuracy of the simple security-based arms race model many policymakers and pundits have adopted to warn about the consequences of an Iranian bomb.
Common sense says a nuclear Iran makes further proliferation more likely rather than less likely, but some perspective is worthwhile. This is also why sanctioning Iran is important whether or not sanctions “work” in terms of getting Iran to do what we want. Countries that are willing to risk economic and diplomatic isolation can get away with a lot of malfeasance, but other countries can be deterred from following malefactors’ lead. Concurrently, one reason it’s crucial for the United States to move forward with our own nuclear disarmament agenda is that to make proliferators pay a real price for bad acts the idea of price-paying has to have legitimacy in the eyes of non-nuclear states—Brazil, South Africa, Turkey, Italy, etc.—and not just be viewed as superpower bullying.