I thought there were a significant portion of Marylanders that fought for the CSA.
It was one of those "Government was with the Union, People were with the Confederacy" kind of states, similar to Kentucky. Many Marylanders did fight for the CSA. If I remember correctly however, the 1st Maryland Zouaves were Union. I might be confusing them with another regiment however, let me go check real quick.
Alright, the a Battalion of the 1st Maryland Regiment for the CSA were Zouaves. Not an entire regiment, however.