The premise is that society has been destroyed and there is nothing left but little groups of survivors. Either you accept the initial premise of the show or you don't. Wanting them to go back and explain the premise a few season's in just isn't what the show is.
Besides, I think everyone is missing the most important aspect of the episode, Daryl is back and saw Merle for what he really is in less than one episode.
Anyone thinking Merle will go the backstabber route and try to turn on Daryl and the rest if he thinks the Governor's group stands to win their little war?