Our Achilles Heel

…the 1776-1783 (American Revolution) conflict contained two strategical problems… The first of these was that once the American rebellion spread, its suppression involved large-scale continental fighting by British forces at a distance of 3,000 miles from the home base… maritime superiority alone could not bring the largely self-sufficient colonists to their knees… To conquer and hold the entire eastern territories of America would have been a difficult task for Napoleon’s Grand Army, let alone the British-led troops of the 1770’s The distances involved… exacerbated the logistical problems: “every biscuit, man, and bullet required by the British forces in America had to be transported across 3,000 miles of ocean” (D. Syrett, Shipping and The American War 1775-1783[London 1970]) … Moreover, colonial society was so decentralized that the capture of a city or large town meant little. Only when the regular troops were in occupation of the territory in question could British authority prevail; whenever they were withdrawn, the rebels reasserted themselves over the loyalists… (How many troops were) now needed to reimpose imperial rule—150,000, perhaps 250,000 “It is probable,” one historian has argued, “that to restore British Aurthority in America was a problem beyond the power of military means to solve, however perfectly applied.” (Barnett, C. Britain and Her Army 1509-1970: A Military, Political and Social Survey. London, 1970 page 225)
Paul Kennedy The Rise and Fall of the Great Powers: Economic Change and Military Conflict from 1500 to 2000

The Vietnamese understood this. The Mujahadeen understood it in the 1980's.

The insurgents in Iraq and the Taliban/AlQaida know that their greatest weapon is time. They're permanent, we're temporary.