Here’s some interesting analysis:
China, France, India, Israel, Pakistan, and the UK all saw declines in their total militarized dispute involvement in the years after they got nuclear weapons. A number of these are big declines. USSR/Russia and South Africa have higher rates in their nuclear versus non-nuclear periods, though it should be kept in mind that for the USSR we only have four years in the sample with no nukes, just as the Cold War is starting.
After accounting for a decent number of variables, the general trend still holds: acquiring nukes is more likely to lead a decrease in military activity rather than an increase. Of course, extrapolation doesn’t prove anything, but the historically observable fact is that acquiring nuke does not automatically lead a country to act more aggressively.
Incidentally, only one government has ever detonated nuclear weapons during war, and that was the United States’ government during WWII. Perhaps, then, foreign policy experts are projecting our intentions onto the Iranians.
Whatever the case, the United States does not have the authority to tell sovereign states what weapons they may or may not acquire. As such, Iran has the right to pursue nuclear weapons if they so desire. The United States, therefore, may find advantageous to start behaving with more diplomacy and less bravado when dealing with foreign powers. Especially if we go bankrupt and can’t afford a military anymore.