James,
Recognition of military service is important. (See my profile)
One of the key issues with the use of categories is limiting them to a resonable number of members. Resonable is hard to define but it is probably less than 100,000 or so.
This is one reason that templates for military are encouraged.
Robert William Husser is one example of a military template -
see Template:Veteran Recognition for use and options.
For Civil War it is possible to add the individual unit - that has not been developed for other wars - perhaps it could be - a lot of work - interested?
Phil