The guide posted below is great if you really want the Achievement, but it really does ruin the game for you. Once you know how to win, there's not much replay value left in this trial-and-error game.
Also there's a lot of luck involved. I've taken Madagascar before but have been stopped by Peru, which borders 3 countries. You can never tell.
And what's special about Greenland?
 "Endless Migration"){kind=icon}
 "Pandemic 2"){kind=icon}