I am curious as to why Sauron went to the trouble of raising a large army to conquer Middle-earth when he could have used the Nazgûl to kill all his enemies in Middle-earth such as all the armies of men, elves, and dwarves.
Nobody could kill them and this included the Istari and Galadriel. All they could do is use their magic to drive them away for a short time. Plus, the Nazgûl had the advantage of not needing to stop and eat and sleep like the Istari had to, so they could have been out killing soldiers during the nighttime hours of each day while the Istari were sleeping.
Why did Sauron need a large army when he could have used the Nazgûl to kill all his enemies in Middle-earth?