when the Afghan defeated the Russians, with help from our CIA, the average age of an afghani was 14.. instead of educating them and providing a humanitarian effort, we abandon them and groups like the taliban moved in to 'educate' these young teens.. now, they are today's terrorists.
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We have the experience of the Soviets, the early Brits and our own in Afghanistan. Nation building isn't a good idea there. After destroying and running off the Talib and al Qaeda, the best bet was to use the airfield at Bagram for a couple of months to round up those we could, give the keys to the government HQ to a strong warlord with the warning, "don't give us a reason to come back."
Alexander the Great didn't do well there either. But, they did name a city after him.