system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly would have to happen to create a 51st state in the USA and why hasn't it happened since 1959?

I sometimes hear people saying they want a North and South California, or that Puerto Rico might become a state, etc. etc. And I'm guessing it's a pretty big deal to make a new state since it hasn't happened in a long, long time?
gpt
Article IV, Section 3 of the constitution covers this.

The short answer for Puerto Rico is that it would take an act of congress to make Puerto Rico a state.  It gets messy in that Puerto Rico would need representation in Congress as well as electoral votes and those would have to be pulled from somewhere else in the Union.  Given that no one wants to give up power it would be quite a battle.

As far as making a new state from a current one or combining states it would take the approval of the state as well as federal legislature to make it happen.  And then the whole mess of votes and representation would happen again.

The short, short of it is there would need to be a massive amount of support at both the state and federal level to make a new state.  Something that just doesn't exist right now.

Locals who agitate for secession to make a new state (like in N. California and elsewhere) are just that:  agitators who have no legal standing to create a new state unless they can convince enough people to make it happen through legal channels.