not only was it long period but the Middle Ages are only ever brought up by people educated by a Western/ized idea of history.
My point stands because we would never hear of systems that "worked" in a decentralized way because required power structures would have never been in place for them to leave any impact that people will feel should be noted in the history books. James C Scott[1] does a great job tracing decentralized societies fleeing the Chinese empire over a period of several hundred years and settling in the hard to access hills of South East Asia.
A successful decentralized society wouldn't be in our history book because the measure of success is different in these systems. In fact things that are a failure in one system are a success in the other.
In the same way today, groups like the Jawara/Andaman or similar tribes will always remain a footnote in our books, at least until their successful assimilated into our own "superior" culture, and then we give them an honorary mention (= by then their way of living is destroyed ofc).
Another way to read this (and the way I personally do) is that a successful decentralized alternative is often the by-product of (an over-reaching) centralized system. Take a look for what the state labels as crooks, outlaws, degenerates, pirates, insurgents, terrorists, or anyone they are struggling to tax and prosecute, ... in modern times Roma/gypsies are the only ones left who come to mind. Everyone else we eradicate!
[1] https://en.wikipedia.org/wiki/James_C._Scott#The_Art_of_Not_...