yeah or a natural disaster, or even an invasion (who knows what the fuck china is gonna try and pull), but much more likely a natural disaster, or a riot
a lot of people dont know what actually happened right before and for awhile after katrina hit - the government literally sent in mercenaries for hire from a security corporation called blackwater - most of these guys weren't even american but were occupying the city in a militaristic style, swat teams were also sent out to the homes of those with registered firearms and took them by force, when a politician was being moved out of the city by a blackwater SUV they came under fire from some random gang members who were taking pot shots at people from a highway overpass, the blackwater dudes rained rounds on them, stopped under the overpass and when they heard screams and moans just moved on, those deaths were never even properly reported through police
i think that last story really paints a picture as to what it would be like in an area without police rule, im not talking nation wide stuff here, that would be insane, who knows what type of shit will pop up and where, being armed could make the difference even in an overnight riot