Forum Moderators: skibum
To use each, you have to sign up for each, and place different links for each, i.e.: If you want to sell to Americans, then sign up with Amazon.com and add .com affiliate links. If you want to also sell to Brits, then you need to sign up separately with Amazon.co.uk and place additional affiliate links.
About 6 months ago, an Amazon rep did say something about the possibility of merging the various programmes in the future, which would be great, but I haven't heard anything about that since.