Mav felt it would be appropriate to pin this and add another link.Q. Can I have more than one UN Nation?
A. No individual player can possess more than one UN nation. The moderators do periodic checks, and throw those who abuse the one UN nation rule out of the UN.
Also, if you share a computer with another person who also plays on Nation States, only one of you can be in the UN. If you both join the UN, when the Moderators notice that two UN accounts use the same IP address, they will throw both nations out of the UN, no questions asked.
So, if you are using a shared computer, you may not want to log in with your UN nation. Only log into your UN nation on a secure computer that only you use.
Edit: This thread describes how they catch cheaters http://forums.jolt.co.uk/showthread.php?t=274575 