I hope you know that there are actually only two manufacturers in the USA now. Seagate and IBM. Does WD make drives at all? If so, where?
Actually, IBM long ago sold the disk drive business to Hitachi Data Systems (HDS).
After Seagate acquired Maxtor last year, there are only two major US makers left in 3.5” drives - Seagate and Western Digital.
Besides Seagate, WD and Hitachi, other major manufacturers include Fujitsu and Samsung and some smaller R&D companies (some US) mostly in 2” drives space and removables.