Where and how, did marshmallows come into being?
Well, when a daddy marshmallow and a mommy marshmallow are in love… 
According to these links, they originated in ancient Egypt, although those sound a little different from today’s marshmallows:
This is a marsh mallow, a plant of the mallow family endemic to salt marshes in Europe and England, and introduced into the Eastern U.S.
There was a confection made from the root of the marsh mallow which produced a sweet, sticky substance with a mild laxative effect. For obvious reasons, much as the root of the potato plant is called a potato, was referred to as “marshmallow.” This in turn gave rise to the modern treat.
Does anyone still make marshmallows out of marsh mallows?
Martians, possibly? 
I had previously wondered what connection there could be between the plant and the goey confectionery. Useful thread!
I have a number of books detailing edible plants and their history; a few of them have recipes for real marshmallows, using the authentic plant, but they generally advise against making them in any quantity; the Marsh Mallow plant is somewhat uncommon, and harvesting them is legally problematic here in the UK - since you have to dig up the root, killing the plant - which you can do with many things if you have the landowner’s permission - salt marshes are often Crown or National Trust properties, and they’re not likely to grant such permission.
I suppose the plants could be cultivated to provide the necessary gum to make the confection, but there’s probably not enough demand to make this worthwhile (and indeed it may not even be palatable to modern consumers of mass-produced confectionery).
One thing is for certain though; if I point at something and tell my kids ‘that’s a marsh mallow plant’, they’re going to smirk and roll their eyes; exactly the same as they did when I told them there’s a number called Pi.
When come back, bring…oh, screw it…
FWIW, the ultimate marshmallow-referencing literary work would have to be Shel Silverstein’s kiddie-lit classic Lafcadio, the Lion Who Shot Back. It’s a long story to recap here, but suffice it to say, it involves African big-game hunting, said lion (named Lafcadio), and his sweet tooth. Let’s just say that *la dolce vita * was never so [bitter]sweet as it was for this alienated, marshmallow-addicted lion.
I just mentioned it because I just love marshmallows – and Lafcadio!
A real marshmallow made with marshmallow root is not a marshmallow as we know it. It’s not soft and pillowy and squishy, for one thing. It’s more like a merengue cookie - crisp bubbles with an unbelievable stickiness. I don’t think they’d sell very well. My students don’t like them much when we make them in herb class.
How fascinating! What do they actually taste like?
Mmmmm, Marsh Mallow Pi.
Sweet. Very sweet. But that comes from all the sugar, not from the marshmallow itself. Marshmallow root extracted in water gives you a viscous slime not entirely unlike snot, but more tasteless. (Slimy yet satisfying!)
If you notice the comment at the bottom of this recipe, they’re nothing like “marshmallows” are. I’m not exactly sure why the marshmallow root was ever baked in a confection, as it has very little taste. It’s so tasteless, it’s easy to get even kids to drink it, unlike horehound, a medicinal which needs all the sugar in candy to make it bearable.
If you’ve ever had a stale merengue cookie, you’ve had an experience pretty close to a “real” marshmallow. Very disappointing.