Attached is an iptables rule set for allowing all IPs from the United States, then denying everything else.
This was generated with the help of this site
http://www.blockacountry.com/
Which is where I got all of the Ips from. That site gave me a list of about 36000 ip blocks. Using a little perl script (also attached) I was able to reduce that to 15000 lines.
Which might work better for those of you whos system has issues loading huge iptables lists.
Share and enjoy.
