An invasion of all world forces include Canada. And you could try to transfer troops trough the north pole (it will be a logistical nighmare) And in Canada you have the energy sources for the war effort.<p>I think that this "military expert" is gravely underestimating the resourcefulness and inventiveness of humanity when it comes to killing each other.<p>You could also do your best to blow up the Gulf Of Mexico oil infrastructure and US is on 3 month lease of life (or an year if it is stretched for military use only) which could make them move on the offence. Add some propaganda to create domestic problems at home ...<p>If you remove the nukes it comes down to oil and humans. US is outmatched in both.