A war with Iran, particularly when the US seems intent on stirring the pot with half a dozen other nations globally, would be an absolute clusterfuck for everyone in the region. But the folks who would pay the highest price would always and forever be the Iranians themselves. I would argue that the biggest deterrent in this would be the Saudis, as they host a bunch of our military bases and are extraordinarily vulnerable to retaliation from a nation they desperately need as an ally to stabilize global oil prices.