<i>Somebody forgot to factor in the effect of an 8000-mile supply line, or the reluctance of a people to give up deeply-entrenched customs.</i><p>That's not the problem.  Britain ruled Egypt for many decades using only 5,000 soldiers and actually turned a profit.  Egypt at the time had 9 million people.  Back in 1900, logistics were even more difficult, and Britain's technological edge was actually much less.<p>The core problem is the the U.S. cultural DNA is anti-imperialist.  No one in state department or DOD has actually read the memoirs from the British empire about how they did it.  Nor is the U.S. willing to use imperialist tactics.  For instance, if you're doing imperialism you need to have a native army reporting directly to the ruling officer class.  Instead, the U.S. is trying to police every street with American soldiers.  Second, instead of encouraging political parties and democracy, an imperialist needs to prevent them.  Political parties incite people to action by blaming other ethnic groups for problems, and they spend all their time worrying about grabbing their peace of the pie.  It's very easy for political parties to turn into actual gangs.  Third, you cannot be afraid to issue the entire population ID cards, have curfews, checkpoints, population control, etc, until the region is pacified.<p>Do the above three things, and imperialism is easy.  You can do it with 5,000 troops and turn a profit.  But do it American style, where you are doing imperialism without admitting it, and you get disaster.