Blizzard has decided that StarCraft II will only feature region specific servers at its release. This just means that American players wont be able to go up against Korean players, putting a temporary hold on the eternal struggle between Western and Eastern StarCraft competitors. Apparently, the servers might open up in a future patch after Blizzard has been given time to fully analyze the situation. This is just so they can ensure that the new matchmaking component can work solidly with a cross-server.
So, sorry to all of the American players who were itching to go head-to-head with people from other regions. For now, you’re stuck playing your neighbors. Hopefully, we’ll see cross-region play integrated into StarCraft II soon.