Why is Puerto Rico not a US state?

Related questions

1. Is Puerto Rico a US state?
2. Is Puerto Rico part of USA?
3. Does USA have periods?
4. Do Puerto Ricans pay US taxes?
5. How many country are in USA?
6. How old is America today?
7. What was the last state to join America?
8. Is Canada larger than USA?
9. Will the US ever get a 51st state?
10. Is PA a red state?

Tags

1. #island
2. #unincorporated
3. #subject
4. #nation
5. #status
6. #residents
7. #puerto
8. #territory
9. #federal
10. #political
11. #united
12. #state
13. #taxes
14. #contrast
15. #neither
16. #income
17. #states
18. #sovereign