Is there a way to exclude all locations in AdWords except the US?
I'm not sure if the only way to do this is the manually add countries that aren't US (I know the limit is 1,000. I'm also aware that you can target your ads).
Geo targeting in AdWords generally includes not just people that are actually in your targeted location but also people that:
If you target to the United States, you may end up advertising to people that view US websites from out of the country.
This behavior of targeting can be changed to restrict targeting to only people who are in the targeted location. To do so, make sure the advanced targeting setting of "People in, searching for, or viewing pages about my targeted location" is disabled.