Just get your passport and go forth, young man.
All of them; however most US Citizens residing in Latin America are found in Mexico.
From the US? It is international travel. If you mean NEW Mexico, that is domestic travel, though.
No.
Yes.
If in Mexico travel north. There is a border crossing. Pass that and you are in the US
IF you are a residence of the US, you abide by the US regulations.
As long as you have an American passport, you can enter Mexico. Problem is on your way back to the US. Without a valid proof of citizenship, you will not be abe to return to US soil.
Yes, provided you have an American passport.
Yes, they do.
Yes.
ye you do
no