The US pulled out of the nuclear deal and applied sanctions. The sanctions are crippling, if you deal with Iran than you can't do business in the US. They have absolutely rocked an already unsteady Iranian economy. Iran has engaged in many provocative acts over past year to try and force the world community to come to the table and improve conditions in the country. Many of these provocative acts have rubbed up against American interests. Aside from working the sanctions as hard as humanly possible the Trump administration has chosen to not too respond. Trump has talked about how he doesn't want war with Iran many times. Iran has been gaining some traction with the world community and had little incentive to ease off. The Trump administration was begining to look weak or passive. I guess the buck stopped when an American contractor was killed. Will Iran back off now that the US has bared its teeth? Will Iran redouble the pressure? Who knows, I don't think the Iranians know. They probably have to respond in some way to save face with their own public and assorted allies but I'm sure someone is trying to figure out how to deescalate the situation. Will both sides take a path that lowers the temperature? The Iranian public has been in the streets, outraged at the status quo in recent months. The government has violently suppressed the protests. We are talking about scores or possibly hundreds of dead, the counts have been suppressed by the government and bodies keep showing up. This is a big problem for the government. The Iranian government is far from monolithic. There are many competing factions. The Ayatollah is old and might be the last Ayatollah who has significant power. The president has been under a negative propaganda assault from the incredibly powerful revolutionary guard who would like to see their own guy in the presidency (I can't remember this guy's name for the life of me, maybe he is the guy we just wacked but I suspect not). Iranians have shown time and again that when the are attacked by outside forces, they stick together. I don't know anything about the guy the US killed and that about all I know bout the Iranian situation right now.