Serious question. How common is it for a group of people to have this level of self determination? Eg if people in California decided not to be part of the US, can they?
Well, if the people of California all wanted to leave, they could elect a legislature and a Congressional delegation that is pro-secession. This is farther than China will allow Hong Kong.
After this, the California Congressional delegation could introduce a California secession bill. This bill would be debated in Congress.
If they were really serious, the Californians could support a constitutional amendment specifically allowing secession sort of like Article 50 of the EU.
But there are other example of people having this right. The people of Scotland narrowly voted to remain in the UK (but could have left). The people of Northern Ireland have the option to leave the UK. The UK chose to leave the EU. Puerto Rico could probably leave the US (who currently rules them) if they wanted to.
If the people of California decided to secede, they'd have the entirety of the US military giving them 24 hours to reconsider or else. If somehow California fought back and held out for a few years, maybe the US would give up and let them go, but probably not without intentionally destroying every single valuable asset that state has.
As much as people like to paint China as a villain here, a very solid proportion would support similar actions in the US.
> If the people of California decided to secede, they'd have the entirety of the US military giving them 24 hours to reconsider or else
Maybe. Maybe not. I personally think the US military would give them a couple of weeks just like they did last time when certain southern states tried to break away. However whether or not the federal government waits a few weeks isn't the main question.
If the people of California held a vote on whether they should be allowed to secede, zero US military personnel would interfere in any way. After holding such a vote, if the California delegation to Congress wanted to, they could force a vote on whether to allow California to secede.
While I would be very surprised if they were allowed to secede, I bet the people of California could win concessions from the other state governments. California elects nearly an eighth of the house of representatives. Combine their delegation with right-wing republicans who might be more than happy to eject California and the House might just vote to lose California. Through all of this, the military will do nothing. The Senate will be harder to convince, because every state has the same amount of representation.
Texas discussed secession recently, as did a few other States. While we did militarily crush the states who tried to leave in the 1860s, they attacked us first. Then we invaded them and brought them back.
