I think the examples you cite are not really cases in which law and order has broken down completely. In Stalingrad, the Red Army ruled with an iron fist. Law and order never really came close to breaking down in Britain during the two World Wars, either.
However, I think you have a point. First of all, a complete and utter breakdown of law and order takes some pretty extreme circumstances. In modern times, one might take Rwanda or the Balkan conflicts (with their "ethnic cleansing") as examples.
Probably the best historical example I can think of would be Easter Island, which suffered a catastrophic collapse a few hundred years before the island was "discovered" by Europeans. I'm not an expert on this, but I understand that this period was one in which the population disintegrated into small tribes, living in highly fortified dwellings. They would venture out to hunt and fish either stealthily (always on the lookout for enemy war parties) or in large armed parties. Always with the risk that an enemy would attack the fortification and destroy it for whatever you had and they didn't.
Realistically, if such a total breakdown ever did occur, those who grab their BOB and take to the hills would probably end up being easy pickings for those who formed into gangs.
Perhaps we should all set up a secret rendezvous ... <img src="images/graemlins/wink.gif" alt="" />
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"The mind is not a vessel to be filled but a fire to be kindled."
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