It all comes down to this. Sauron and his forces await you in a stronghold to meet in battle. Your followers will be present to help aid you in the fight as well. After you dispose of Sauron, he will resurrect fallen Warchiefs you have previously slain and you'll have to reengage them a second time. Not only will you have to deal with 5 Warchiefs at the same time, but Sauron will be also trying to end your life. If you manage to accomplish this feat, you'll be rewarded with an interesting cinematic at the end!