There's a reason there are no Anarchist regions on the globe. And it's the same reason there never will be.

I can't really play the devil's advocate here. I don't think supposed anarchists actually believe such a system could be actualized nor do I think they actually believe it would "work" by any measure for any period of time.

Law and social contract theory are not new. But they don't function without systems in place to ensure that they are actualized. When someone steals your bread you don't appeal to the community to recover what might be recovered and punish the perpetrator(s). If you had to do that, nothing but a sense of decency (which it would be silly to presume everyone had regarding stolen bread, seeing as there are people willing to murder billions--and some have even managed to murder millions) would discourage people from stealing bread. Theft of bread would be more common. This, of course, would discourage the production of bread, considering it's value in feeding oneself and one's people and value for trade would diminish, since stolen bread has no value--it is not in one's possession to consume nor trade nor anything else.

The point being, of course, the paramount importance of law and enforcement of the law. There's a reason there have been laws and law enforcement for tens of thousands of years. Law enforcement, even as envisioned by "anarchists," involves the association of men who make agreements and take action for their common good. And this is government. I say that I don't believe supposed anarchists actually believe such and such about their desired state of things because, ultimately, it seems they're just saying something about what sort of government they would like in place. Because, no matter the stated starting point, some sort of system (government) naturally occurs out of the associations of men. The theoretical starting point is irrelevant. X number of people can theoretically live in peace and harmony without a government. But X number of people live on earth, not a vacuum, and sooner or later they can form a government to defend themselves or be subjugated by outsiders. In either scenario, 100% of the time government exists. 0% of the time does a stateless society persist for more than moments in an isolated community.

Anarchists may refute my claims at any time by pointing out a 'successful' (by any measure) anarchist, stateless region of the globe any time in the earth's history. There aren't any. Happy hunting.

"How did anyone fare fighting tanks with the horsemen and lances in (I think) Belgium?"

Perhaps I misunderstood you, but it's my duty as a historian to dispell legend from truth. The myth of the (Polish) cavalry battling German tanks is untrue. It originated from images of the raid attempts the British cavalry tried in the early parts of WWI while being blown to bits by German artillery. It was a state of the art cavalry though, and their horrible losses was more or less the end of any cavalry in the western world.
The Polish did have a cavalry in WWII though, but they didn't do large scale attacks against German tanks.

We had a lecture in wich that myth was proven false. It was a rather popular myth though. I'm not saying there weren't any attempts to destroy a tank with cavalry, it might have happened. But there was not a single large scale attack against a panzer-division, like the myth tells.