It sounds like the start of an excellent nursery rhyme or often overlooked college course, "what is gin made from?"
The answer is vodka.
Gin is made out of vodka. It was vodka, and then they added flavors, most notably, juniper and that is basically gin.
The absolute basics are: any liquid sugar ferments into beer or wine, a beer or wine can be distilled into a spirit. Remember, distillation doesn't create alcohol; it just removes what ain't booze from what is. That spirit is just raw alcohol, in the case of wine, it's in the extended family of brandy (grappa, pisco, Cognac, Calvados, etc.), with beer it's in the massive family of grain alcohol (whisk(e)y, rye, Scotch, Bourbon, etc.).
Vodka is made from any fermented sugar. Vodka was likely made initially from rye or wheat— potatoes didn't make it to the old world until six centuries after the advent of vodka. Contemporary vodkas can be made from, any cereal grain, sugar cane, or any fruit imaginable. The cheap stuff is mostly made from corn.
Though the origin of gin wasn't buying bulk vodka and flavoring it with juniper, that is how it's mostly done these days. Gin distillers purchase neutral grain spirit (vodka before they water it down) and flavor that neutral spirit, which can be made from anything, with juniper and other botanicals. Adding the juniper flavor to a neutral spirit can happen through many different production methods, but let's just hope they are re-distilling the neutral grain with dried juniper berries.
Juniper berries are incredibly acidic and bitter. Products aren't made from juniper; they are flavored with juniper.
So, again, what is gin made from?