And that gets to the fundamental problem: The current regional system was built without Iran—in some cases built in opposition to it, and in some cases simply bypassing it. The system will have to adjust to admit Iran, and Iran will have to adjust to be admitted. But with Iran’s influence having grown enormously over the wreckage of Iraq and Syria, historically regional powers in their own right, adjusting and finding peace may allow Iran to make disproportional gains relative to its neighbors. Iran has effectively bought Iraq and Syria on the cheap as fixer-uppers. They’re enormous security and financial liabilities for Iran right now, and will remain so as long as the neighborhood can’t agree on settling their conflicts. But if that agreement comes through, the value of Tehran’s investment will skyrocket, and they may find themselves looking for new ventures. That’s not to say that we’d see the Islamic Republic moving its capital to the ruins of Ctesiphon and proclaiming the restoration of the Persian empire. A restored Iraq and Syria would not be puppets, as their renewed strength would allow them to pursue their own interests. But Iran could enjoy deeper influence and friendship with both than it has had for centuries. This would be a major alteration of the regional balance, and it would be very unfavorable to countries that have the power to play spoiler. Iran’s growing power would work against it.

And we haven’t even mentioned the role of the United States here, which, for all the talk of grand bargains, would face both internal political constraints and external pressures from its allies in shifting toward Iran. We’re not exactly the best at understanding other countries’ interests, either, and the lack of diplomatic contact with Iran—now apparently amplified by Khamenei’s latest ukase—doesn’t help.

All this means that there are high structural barriers to Iran reentering the regional system. The nuclear agreement only addresses these barriers indirectly—by stopping the economic damage of sanctions and creating the possibility of fuller cooperation with Russia and China, it can eventually make itself stronger. But as long as its neighbors see that strength as fundamentally threatening, it will only be able to make gains using naked force. The Iranians may soon discover the truth of Chesterton’s adage about fascism: used alone, without legitimacy, raw power “is the weakest thing in the world.” In regional geopolitics, the deal is simply not that big of a deal.