The prophecy against Moab is a two part prophecy.  The first part takes place during the Kingdom of Judah (before it was conquered by Babylon) and speaks of the literal destruction of the kingdom of Moab which has been fulfilled.  The second part, the ultimate and final fulfillment of this prophecy will come during the end times when Moab (modern day Jordan) is destroyed once and for all, and the land becomes part of Israel.  Later on this newly acquired land will be used by Israel as a hiding place (Petra) for the Jews during the last half of the Tribulation.