This was bound to happen, with a lot of US military buildup that was going on all while Iran was kept on negotiations but the nuclear deal wasn't gonna happen. I wonder if Iran already knew ahead that they are preparing to attack and had made preparations. But seems like Iranian military has been crippled badly in the last skirmish and hasn't recovered from it.
What's gonna happen now we don't know. Trump said that regime change is on their highest priority and therefore firstly, US and Israel will focus on taking out Ayatollah and IRGC as well as taking out ballistic missile sites and trucks. Secondly, they will focus on taking out or taking over Iranian nuclear sites either through bombing or maybe spec ops teams doing the thing. Thirdly, if the situation calls it and the regime collapses, then they will bring in the Shah Pehlavi to take over.