I love family history databases with millions of names in them. They make research so rewarding! One such data source is CWSS -- the Civil War Soldiers and Sailors System, maintained by the National Park Service. With more than six million names in the system, CWSS gives you an immediate sense of the vast scope of the Civil War. The entire population of the US at the time (North and South) only came to about 32 million or so.
CWSS shows the information on the General Index Card...an information source prepared from unit and regiment musters as a soldier or sailors service record.
The cards were also used after the war to figure pensions for Union Soldiers. Once you identify the microfilm role with a record of interest, an actual copy of the General Index Card can be ordered from the National Park Service.
Don't forget to check for your family history at Ancestry.com and NewspaperArchive.com. Yes, these are subscription databases, but they are also among the most powerful research tools available for looking into family roots.