Northern Afghanistan is dominated by Tajiks, Uzbeks, and other ethnic groups that were a mainstay of the mujahideen forces that fought the communists, and then fended off the Taliban until 1998, when the Islamic extremists captured and held Mazar until the US intervention in 2001.
Decades ago, however, pockets of Pashtuns moved into the region, encouraged by the central government, and many of these Pashtun areas have become focal points for the Taliban's northern insurgency.
Insurgent activity is still far below the levels in the more violent provinces in eastern and southern Afghanistan that are expected to be the recipient of any new US troop deployments, but some analysts say the north shouldn't be overlooked.
If the international community reinforces the Afghan police and military there, "the insurgents could be stopped relatively easily. This will not be the case in one or two years if the insurgency is allowed to grow," wrote Gilles Dorronsoro in a report for The Carnegie Endowment for International Peace.
Some of the biggest Taliban gains have been in northern Kunduz province, where insurgents set up shadow governments in at least one district. Earlier this month, some 750 Afghan and international forces launched an operation that reportedly killed more than 100 insurgents, including eight commanders, according to NATO officials
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Across the country, in northwestern Faryab province, the Taliban have moved heavily into one district that's predominately Pashtun, according to US Army Capt. Samuel Weeks, who commands a company of US soldiers based in the province's capital city. Just before the Aug. 20 election, mortar attacks in the Faryab district killed seven Afghan police.