Question : How to block all IP addresses not from the USA>

I have  been task with blocking all IP  addresses not from the USA from our system.

I am looking for suggestions on the easiest way to set up our ASA5510s.

Answer : How to block all IP addresses not from the USA>

This is true, it is not easy to dierctly and accurately correlate geographical location to IP address, much less large blocks of them.

Aesources which may help a lot though:
http://www.iana.org/numbers

More specifically:
http://www.iana.org/assignments/ipv4-address-space/ipv4-address-space.xml
and
https://www.arin.net/knowledge/ip_blocks.html