It won’t be global unless Israel/US bombs Europe
Incorrect, if Israel/US pre-emptive strike Iran with a nuclear weapon as a """last desperate measure""" then russia will immediately follow suit and use nuclear weapons on Ukraine. This may or may not remain limited nuclear escalation, but even if it doesn't there is the grim natural facilitation of Putin's power AND the US/Israel's power if this tit for tat is allowed to happen.
None of this has to make sense logically for it to happen, Stephen Miller is the kind of rightwing scary you wouldn't leave alone with your kids....
The US will not invade Iran in any general or broad sense, what Trump/Vance/Israel/Putin want to do is reach for the easy "game over" button to these conflicts/shows of power/"mowing the grass" episodes.
The US can continue to destroy a reasonable future for Iranians though, will it accomplish anything? Yes, the US needs a villain and if you subject people to enough undeserved trauma people are likely to eventually turn into what you perceive as villains, which is the clear point of the Iran War -> to ensure Iran doesn't threaten to try to integrate to the greater region and world in a peaceful manner and that it succombs to a militant obsession with fighting Israel/US instead. I.E. "mow the grass"
The only way to interpret the actions of the US and especially Trump/Vance here is to conclude they are desperately trying to craft an Iran government and culture through acts of mass terrorism against the Iranian civilians that can put on the clown suit somewhat for US/Israel bigoted world views of who Iran is and why they justify all of these sacrifices we "have" to make to our futures at home.