Marc,

When you look at European landscapes most of the forests have a manicured look. Sit down on a weekend and watch the hunting shows and the european hunts have that same look as a nice American park.

I live in a metropolitan area in the northern midwest. You walk 100 feet out my back yard and you can run into bears, deer, coyotes, raccoons, and you are in deep forest. A fair chunk about the size of a small city with it's own ecosystem.

With the changing population migration patterns and more people moving into cities the general concepts of frontier are being lost. Even suburbia is loosing the more wild feel to it. People in general are becoming more removed from nature, scope, scale, danger, and so much more. Take a city dweller into the woods and watch them stumble around. These are people who stumble on a raised edge of a sidewalk crack. Ask them to judge distance and they are done for.

Even the northern United States and Canada (what 2/3rds of the Canadian population lives within 100 miles of the US border?) they are becoming less able to deal with the aspects of frontier environment. Consequently areas that had been "civilized" are now returning to nature in some perverse twist.

All of that to get to here. Consider northern Canada and especially the Northern Rockies and mechanized transport is not going to happen. You can't fly jets into those box canyons and even missiles are of nearly no use. Yet you could hide an Army in there for a long time. Outside of Hope, BC you could interdict the entirety of the cross Canada rail road pretty much at will if so desired (and as done by the Cree in the 90s). A lot of the same skills that you might expect in Afghanistan would be required to fight in that area.