Can you just get fired in USA?

MK

I've been reading left and right about the mass firing of Twitter employees, which makes absolutely no sense to me, i don't really care about the reason or the whole Musk buying Twitter drama, i just don't understand the concept of a manager or a new business owner waking up in a bad mood and just firing people ? That's literally illegal. I live in New Zealand, my manager can't just do that unless maybe i don't know, i slap him ? Or publish confidential info ? The company needs to go through offical restructuring of all teams in order to determine who is staying and who isn't and that's also an official process that is protected and monitored by labour laws and that's not just in NZ, this also applies in Australia, some Asian countries and most of Europe and some middle eastern countries.

So my question is it legal for anyone to just fire anyone without a cause ? If not why aren't those people suing the shit out of Twitter's management?

Again i don't care about this whole Republican vs Democrats drama, I'm talking about general labour laws.