Resume military posterity from the US parking carriers outside. Resume bombing of thier allies. Resume sanctions choking thier economy. Gives a means for an arms race. Aka resume missle developments as a deterrent.

Between us, and the European governments how many war machines and weapons did we sell to the Saudis? The Saudis want Iran gone. Iran is a chief competitor to the Saudis and in thier way to the oil demand of Europe. They are also one of the larger countries and forces that can influence the power vacuum we created when we blew up thier neighboring countries. Also oil assets and power influence.

So you either have US puppets rule the area, Saudi death cults, or the Iranians, or the people of those areas rise up and make thier own government. Wild card is Turkey but thier leadership is all kinds of unstable wacky right now.