there is far more of us than them. If it comes down to it we in the USA are so spoiled that we would turn against our own government and take them down.
I like to call it "The Birds" theory. In reference to the Alfred Hitchcock movie "The Birds" where a bunch of crows attack humans.
Ever been on a beach by the ocean and see hundreds of birds gathered and wonder 'what if all those birds decided to, as a group, attack the human trespasser'? A human wouldn't be able to defend itself against those odds.
Our government already uses fear-mongering techniques to get all of us to get flu vaccines and more recently warn women that if they don't get vaccinated against cervical cancer they will get it later. Just remember these are the same people that decided that inhaling the dust created by the Twin Towers collapse was OK.
What could we do? Seriously, if the government declares Martial Law and uses the military against us I don't really think there is much we could do except wait and die. Hopefully our congress will not allow this to happen.