Joining the Union

I was thinking today...
How hard would it be for another country to just.....join the Union? You know, the United States of America? What if Uzbekistan or Djibouti wanted to become a state? Could they? What if they wanted to pull of a Puerto Rico and just become a territory? What would they have to do?
Would they have to go through a major screening process first? Or....
Would they simply have to say "We want in." then have their citizens vote on it?

As far as I know, there is no actual limit to how many states our union can have. The only thing is that we would have to spread out the representatives and senators a bit more. That is capped at 535. (435 reps and 100 senators)...so.. I am not certain how that would work out.
Depending on how many people join, redesigning the flag could be easy, or it could be hard.

Still, though, could they do it? Could they just give up their sovereignty and become a state?
This means that whoever is control of the country would have to step down. In theory, we could let them be governor until a new one was elected.

Maybe Luxembourg finds this opportunity attractive. Perhaps the Icelandics are thinking about it right now!? I mean...look at the Afghans and Iraqis...they are feeling the hurt right now of what it is like NOT to give in to our demands. I bet being a PART of the demanding side looks pretty nice at times...especially to the smaller nations.

Just a thought.