Historically, it would appear that the entire concept of law derives from Mesopotamian regulations regarding the distribution of an alcoholic beverage produced by following the lyrics of the Hymn to Ninkasi (oldest known recipe for anything). That beverage was more or less what we would call beer, but a bit more complicated and without pressure vessels and usually consumed via a gold straw (I suspect there was also a cheaper tool) in mid-ferment.

So the entire government, historically, is a branch of the BATF. But not the tobacco or firearms part.

This is an odd species, in case you hadn't noticed.