One of the things I find interesting about the American biscuit is that it’s name tends to change depending on the leavener that’s being used to raise it. Look through just about any really old cookbook (written before, say, 1860 or so) and you’ll find all kinds of recipes for “soda biscuits” or “baking soda biscuits”. After that date a lot of “baking powder biscuit” recipes start popping up. My grandmother, in fact, called her biscuits “baking powder biscuits”. Probably because that’s what her mother called them.
Which is not to say there aren’t any soda biscuit recipes still around. You can find them, though in most cases their name has been changed to “buttermilk biscuits”. Why is that? Soda-based baking needs an acid ingredient to initiate the leavening reaction. For most people living in the early 1800’s that was either clabber (a kind of thick sour milk that’s high in lactic acid) or buttermilk, the acidic liquid left behind after butter has been churned out of cream. Clabber of course isn’t around much anymore, but buttermilk certainly is, and over time the terminology just evolved that way. “Buttermilk biscuits” certainly do sound a lot more appetizing than “soda biscuits”, after all.
Of course, now that baking powder is everywhere, you don’t actually need buttermilk to create leavening. But some people still prefer a tangy buttermilk flavor, which is why recipes for buttermilk biscuit recipes are every bit as common as the baking powder versions.