It is my observation that liberty is considered highly valuable and highly important in western politics today and historically. I can pull out any number of quotes from the american revolution to demonstrates how people regarded liberty highly, but I can say we have comments from the trial of king Charles I saying "For the people. And truly I desire their Liberty and Freedom as much as any Body whomsoever. But I must tell you, That their Liberty and Freedom, consists in having of Government; those Laws, by which their Life and their gGods may be most their own. It is not for having share in government (Sir) that [9/10] is nothing pertaining to them." So it seems that even going back to the 17th century, liberty becomes a political value. I can say that liberty was not a peculiar concern of more ancient writers such as Plato, Aristotle, and Augustine, at least in my study of them.
Why the shift in attitude? Is there a reason liberty came to be valued so highly? I do not necessarily wish to go into historiography, but I do want to know if historians have traced when and where political rhetoric about freedom and libery became commonplace.
I want to respond as to why you're not getting responses. The word, "liberty" and it's latin root, libertas has changed in definition over the expanse of "Western" history. Plato, to my knowledge doesn't talk about liberty a whole lot, but I'm relatively sure Aristotle touched on something similar applying the term eleutheria. Augustine is, first and foremost a theologian. While he is certainly foundational to European thought, he wasn't particularly politically minded in the way you're thinking about it.
Cicero employed libertas in a more political sense, but also in the sense of freedom of action. In my own studies, libertas was essential to Genoese political rhetoric, but it's not necessarily liberty as you define it and certainly not how how King Charles defined it. I would encourage you to reframe and resubmit your question if you want a more definitive answer.
Also, this is a huge question, you may need to get into the historiography as any answer will be messy.