i concur with the earlier statement about invading our mainland...impossible...a land force could never get to us
seriously, i've thought about it...now, i live in the usa, so i'm biased, but feel free to tell me the weakness in my idea
sure, you can nuke and bomb, but then the land is ruined
and to bomb us more strategically, you need to have a launch platform close by, in the ocean...which would get annihilated by our fleet of subs, carriers, etc.
but let's say someone rivals our ocean might, and gets close enough for the tact missiles and bombing runs...at that point, we got our land-based defenses in range to make strike
ultimately though, yeah, we could get bombed to hell with enough force
but i dont think we could gever get occupied (occupying the rubble of what used to be the USA wouldnt count...and really, dya think that the aggressor would really be left standing at that point? "sir, we're being bombed alll over the place! it's all over! ahh!" "ok, press the button" NUKES, boom, the end of that
so, to occupy us, they'd have to get land forces over here...they'd have to truck them by sea or air; both options would have to fight through our defenses there
but even if they got land troops on our soil, they wouldnt be able to get them there quick enough or in enough numbers to be useful....too many would die before the rest arrived...china's million man army isnt a threat to US, cuz they cant use that army on us...it's impotent...unless they all swim real well...
only option is to land them in another country that is land-locked with us, and that would be impossible to keep secret "wow....sure are

of chinese people (or whoever) in venezuela (or wherever) these days, jim"
and i've long imagined the results of invading troops trying to take a city like LA or new york...man....sure, they'd prolly EVENTUALLY kill all the civs and such, with tanks and whatnot, but youre in trouble when you peek around a corner and there's the glint of scopes, binoculars, and various weapons pointing out of every single window in that building over there; urban fighting is possibly the deadliest, so many hidey spots
america's danger lies in stretching our necks out too far, and losing the money game; attacking other countries to drag us into it is likely the best way to hurt us...and the best way to use land forces against us, if that's your particular strength (trying not to pick on china, but it's the one ya hear about

lately, other than n.korea...and dammit, why cant china just back off of tawaiin? that's a war waiting to happen....)