the one driving factor behind libertarianism is the non-aggression principle, or the NAP. the idea is that the only justified use of violence or force is to respond to someone else's violence or force. in simpler terms, "do no harm, take no shit." the problem is how you define "harm" and "shit" which is how you end up with right libertarians and left libertarians who each see the other's "taking no shit" as the initial "doing harm"

if John Nestlé (name chosen for no particular reason) comes to town and takes all the water in the lake, bottles it up, and sells it, and then people start dying of thirst and fight to get their water back, who is doing harm and who is taking no shit? left libertarians say that the townsfolk are well within their rights to get their water back, but right libertarians would say John Nestlé's business is well within it's right to defend itself from them. both of those viewpoints come from the non-aggression principle, just going in with wildly different postulates. right now in america the capital-L Libertarian party is mostly right libertarians, so the term has come to be synonymous with them here

if you consider hierarchies to be a form of violence and believe that the only justifiable use of hierarchy is to destroy hierachy, then you are an anarchist and a libertarian. but with the conmotation the word has come to take on, they would certainly avoid calling themselves that