While the Witch-King established Angmar and battled the 3 kingdoms of Arnor, what were the other 8 Nazgul doing? Were they helping him or did they have other tasks? It seems like they could have been a great help, being super scary and all.
There doesn't seem to be much information about this. There are two relevant entries in the Tale of Years:
- TA1300: ... The Nazgul reappear. The Chief of these comes north to Angmar.
- TA1980: The Witch-king comes to Mordor and there gathers the Nazgul.
The war between Arthedain and Angmar is described in some detail in LotR appendix A parts (iii) and (iv), but I can't see any mention of the other eight Nazgul. Therefore I think we can conclude that they were not involved here. We might speculate that they were active elsewhere, stirring up other enemies of the West (e.g. the Wainriders, who began their attacks on Gondor in TA1851). The entry for Nazgul in the Complete Guide to Middle-Earth (usually a reliable source) says that
The other eight remained in the East until about 1640, when they secretly entered Mordor and began to prepare that realm for Sauron...
This makes sense (the Great Plague struck in TA1636, weakening the watch on Mordor), but I can't find canon evidence to support it.