In response to threats posed by a nuclear-armed Egypt and Saudi Arabia, it is possible that other nations would in turn attempt to develop nuclear weapons of their own. In this way, a nuclear-armed Iran could potentially set off a regional nuclear arms race—which would result in widespread international insecurity. Furthermore, a nuclear-armed Iran would cause Israel to seriously consider ordering an airstrike against Iranian nuclear facilities. An Iranian retaliation against Israel or Gulf states would likely propel the region into war, also potentially drawing the in US and other international powers.
This is not necessarily the case. Iran’s increased regional prestige could influence other nations to adopt policies of accommodation toward Iran, causing the region to stabilize as a whole. This possibility is less likely, but it should still figure heavily into US policy considerations: developing an overly aggressive stance toward Iran overtly or through proxies could eliminate any possible stabilizing regional effects of a nuclear-armed Iran.
Finally, it is unclear how regional proxies including Hizbollah and Hamas would be affected by the creation of an Iranian nuclear bomb. It is possible that their organizations would engage Israel more aggressively than before, knowing they are backed by the support of a nuclear power. While less likely, it is also conceivable that Iran would oppositely cut them loose having achieved its nuclear ambitions. As organizations with legitimate support bases within local populations, such a move from Iran could cause Hizbollah and Hamas to moderate their tactics in an attempt to avoid alienating their local support—on which they would be more directly dependent in the absence of Iranian funding. Either extreme seems improbable; Iran will more likely continue to fund proxies in an attempt to slowly exacerbate the Israel-Palestine conflict from afar.
In the event of a nuclear-armed Iran, the following four policies executed in conjunction will enable the US to attempt to increase the security of the region, while avoiding disrupting any existing stability.
The US needs to work with all regional states to develop multilateral security agreements. These agreements will only be successful if all major parties are included, otherwise there will be gaps in the regional security system. These agreements will work to reconstruct a concept of regional security, while if an Iranian bomb has somehow made the region more secure through accommodation policies, the agreements will be unlikely to disrupt the new balance.
The US must avoid siding with one power or another in an attempt to balance Iranian power. While Saudi Arabia will likely aggressively pursue US support to become the preeminent balancing force against Iran, the US must refuse this possibility. A nuclear-armed or otherwise excessively empowered Saudi Arabia would further exacerbate regional insecurity and alienate other Gulf states. Additionally, it is impossible to predict what Saudi Arabia would do with a bomb further into the future.
The US needs to redouble its efforts to prevent weapons proliferation. Egypt in particular will be susceptible to a strong public drive to develop a weapons program. Regional security crises will be compounded if Egypt becomes nuclear-capable. It is unlikely that the US will be able to perpetually enforce nuclear nonproliferation agreements into the future while tacitly allowing Iran to remain nuclear-capable; at the same time there is little chance anything will be able to convince Iran to disarm. But keeping Egypt—as well as Saudi Arabia—from building bombs will buy time for the US to build up multilateral regional security agreements.
The US must dissuade Israel from using force against Iranian nuclear sites. Iranian retaliation against Israel or Gulf states could result in the outbreak of a regional war, which would potentially draw in the US or other international powers.
Ultimately, the US must avoid shortsighted policies that aggressively ally with one side or another. It is difficult to predict how current allies or adversaries will align themselves in the future; to build a lasting stability, all regional parties must collaborate toward a multilateral security agreement. At the same time, the international community faces the difficult task of discouraging other states from developing weapons programs of their own in response to Iran’s actions.