The Afghan police and army are slowly giving way, despite the United States spending 13 years and tens of billions of dollars training those forces. When the United States completes its withdrawal from ground combat at the end of this year, this unfavorable trend will undoubtedly accelerate -- that is, if the Afghan security forces don't collapse altogether, as did similarly U.S. trained Iraqi forces in that country. Thus, in the longest war in American history, the U.S. military has failed to pacify Afghanistan -- as had the mighty British Empire three times in the 19th and early 20th centuries and the Soviet superpower more recently in the 1980s. In fact, an outside force has not pacified Afghanistan since Cyrus the Great of Persia did it in ancient times.
Why did the United States have the hubris to think it could succeed in taming Afghanistan, when all of these other strenuous efforts had failed? Because many in the American foreign policy elite, media, and citizenry believe in "American exceptionalism."