Orcs of Mordor
The Orcs of Mordor were the orc footsoldiers of Morgoth's lieutenant Sauron. After Sauron established himself in the Black Land of Mordor, he took under his command countless Orcs that continued to battle with Elves and Men over many centuries.
The Orcs of Mordor were not simply gathered from the remnants of Morgoth's armies, but were also bred anew by Sauron. There were many types in the service of the Red Eye, but the largest and fiercest were the Uruks of Mordor, black Orcs of tremendous strength and ferocity first seen about five hundred years before the end of the Third Age. It seems that Sauron could breed armies of Orcs with enormous speed when they were needed. According to Aragorn, for instance, it had taken just a few years for the Orcs to multiply in Mordor to the vast hordes seen in the War of the Ring. Orcs made up the backbone of the Eastern hordes during this War, supplemented by Easterlings, Haradrim, and monstrous creatures of Sauron.
Following Sauron's final defeat at the end of the Third Age, Western forces cleared the Black Gate and surrounding hills of Orcs easily without their master to guide them, though it is suggested many escaped into the vast wastes and steppes of Mordor's eastern lands.