The United States has a geography that until recently worked greatly in our favor. Although the U.S. isn't an island nation it might as well be. Two vast oceans, a friendly country with great tracts of wilderness to the north, and southern neighbors that have been largely under our sphere of influence with the isthmus of Panama serving as a natural choke point. It's been hard to attack us unless you drive a truck bomb into buildings or commandeer airplanes.