U.S. led strike would destabilize the entire region, especially with Iranian response
A U.S. strike would likely produce significant spillover risks as well, including: much higher oil prices at a precarious time for the global economy; the possibility of Iranian and proxy retaliation against Israel leading to a wider war in Gaza, Lebanon, or Syria; and the prospect of American allies in the Gulf entering the fray. A unilateral attack against another Muslim country would also further destabilize a region already caught up in the turmoil of the Arab Spring. And, by allowing Iran to play the victim and demonstrate its “resistance” credentials through retaliation against the United States and Israel, a strike could help resuscitate Iranian “soft power” across the Middle East at the very moment when Tehran is facing historic isolation and its only state ally in Syria is wobbling.
Ultimately, if the United States and Iran go to war, there is no doubt that the United States would win in the narrow operational sense. Indeed, with the impressive array of U.S. naval and air forces already deployed in the Gulf, the United States could probably knock Iran's military capabilities back 20 years in a matter of weeks. But a U.S.-Iranian conflict would not be the clinical, tightly controlled, limited encounter some predict, and the prospects for further destabilizing the region would be high.
Regardless of whether the U.S. or Israel initiates a strike against Iran, Iran is likely to strike back against Israel as well as escalating its overseas operations against U.S. and western interests which will only escalate the conflict to a broader regional war.