They don't need to control everybody, just the survivors.
I think that if martial law is declared in the US it will only happen in response to some major event. If this is disease or bio-weapon related then that would easily be reason to declare certain areas 'abandonement zones' as mentioned, and would also justify the use of extreme measures in general population control.
Along with this it would also seem more justified in the eyes of the people and, as always, patriots will obey their authorities in such circumstances.
If martial law had been declared in New York after 9/11 there'd probably be as much patriotic support for it as resistance, especially if there was a story to go with it, like, "We've got word there are still plots in development", and so on.
Don't forget elites like Bush Sr, Cheney, etc. also have their own personal SS in the form of their
Blackwater Mercenaries and others (Blackwater is approx. 190,000 fully equipped hardcore war fans).
The elites don't have to call on official gov't forces to be able to wield military force.
They have their lists of people to round up. When a situation of martial law is declared, in the initial period of civilian dumbfounded obedience in response to the scare of whatever threat has precipitated it, will be when these forces go and round up the leaders and noted members of groups that they know will resist the official martial law forces.
By the time the general population ever realise what is really going on they will have no leadership to guide any united resistance, and can be controlled more easily... especially if population levels have been drastically reduced by bioweapons, etc.
At least in theory...
...but never fear, the North American Union will be the salvation ...the Phoenix rising from the ashes of the old USA...
