It's pretty much unenforced conscription and a way to track the current body of what constitutes a US "militia". Registration is mandatory and failure to do so

It's pretty much unenforced conscription and a way to track the current body of what constitutes a US "militia". Registration is mandatory and failure to do so is punishable by jail time and/ or fines. If we had another draft in the US, this would be the list used.