> What are they trying for? Regime change in Iran?

Seems like it. I can't imagine what else they might try for.

I suppose USA might think some shock and awe will result in iran making concessions at the bargaining table, but that seems unrealistic to me.

> No more Iranian nuclear program? There barely was one before.

That seems very debatable.

> Keeping Israel safe? It's been an open secret for years that Iran is not a real threat to Israel, because any action it took against Israel would be existential for Iran and its leadership.

Well they did take action against israel (you could say they were indirectly responsible for oct 7). Now they are facing said existential threat.

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Ultimately though. Iran has been a major threat to both israeli and US interests, largely by funding proxy groups that take violent action against those interests. That's your motive for a war.

Iran is currently weak, facing multiple internal and eexternal crisises.

A war is happening because there is a limited window where iran is weak but the window potentially won't remain. That's the reason behind a lot of wars in history.