Well, I know you said only conventional warfare but one of the things that would be a huge factor in any attempt to invade the US is the fact that well, unlike most of Europe the average Joe can own an assault rifle, and people know how to use them. There are something like 200 million guns in circulation in the US (including all types of firearms). However, because of this I believe the manpower pool in the US would be more capable(since most americans know how to shoot a firearm) if both sides started a draft (which in this type of all out war it would be required)
End of 2009 Predictions (Set, January 1st 2009)
Wii- 72 million 3rd Year Peak, better slate of releases
360- 37 million Should trend down slightly after 3rd year peak
PS3- 29 million Sales should pick up next year, 3rd year peak and price cut
