it's a pretty popular thing to humanize and give everything a personality in japan. from ps2's, windows systems, food, toothpaste <_<....why not entire nations :P
Afganistan Afugan-tan. Tan, even more childish, and cute, than -chan. So he made some characters about them and did some pretty sloppy history work and wrote some strips that had funny sight-gags or other cuteness.
If it's suppose to end in Japanese surnames: Merikan should be "Ameri-kun." Russian-tan should be "Ras-chan." Britain-tan should be "Brit-tan." Nippon-tan should be "Jiya-pan" and be the exception.
