Same procedure back then. Get yourself some high proof alcohol. Add Juniper berries, and maybe some other herbs/spices. Water down. And that's Gin.
Edit: Obviously there are dedicated manufacturers producing whisky, gin etc. - but they are at a smaller scale.
It's disgusting to me because I have always seen alcoholic drinks as something holy - just adding ethanol to water sounds like something deserving of the wrath of the gods.