And most people these days live on very small plots of land. Certainly not big enough to grow enough food to sustain ourselves. So once the local supermarket runs out of food, we'll all be eying the prairie dogs and pigeons.
Granted the larger urban centers will be a mess for a while, but we have more than enough energy to run this country for as long as we have to if we use it. We still have enough manufacturing capability to get us over the hump, might have to live off of corn bread, rice and beans for a while but we can easily support ourselves if we completely isolate the rest of the world and let it go to hell in a handbasket.
I own a tool and die business, like the other tens of thousands of small businesses around the country we can do just about anything if we actually get off our collective asses and decide it needs to be done whether or not its politically or environmentally correct to do so.
We also have the great north of Canada to tap into if we need it as well.