"Only the District of Columbia prohibits civilians from carrying a firearm."
That is more than a bit misleading. Several states make the process of obtaining a license to carry so onerous and expensive that few people will ever obtain or qualify for one. Even Maryland, relatively late to the extreme gun control position, has for years required applicants for a carry license to either prove that they may be a target (they carry money as part of a business) or to prove that they have been threatened and are in imminent danger from specific persons, and that the threat will last for a known and specific amount of time.
Even people licensed to carry as part of a business cannot carry except when actively engaged in that activity.
The law has several exceptions, such as going to and from a shooting area, but the gun has to be away from the people in a vehicle, usually defined as unloaded and locked in the trunk or a box.
So, in theory, MD allows concealed carry. In practice the state police have been ordered to make sure very few do. Political influence has often been alleged, but not at this time proven.
Jim