KABUL, Afghanistan — The Taliban insurgency has spread through more of Afghanistan than at any point since 2001, according to data compiled by the United Nations as well as interviews with numerous local officials in areas under threat. In addition, the United Nations Assistance Mission in Afghanistan over the past two weeks has evacuated four of its 13 provincial offices around the country — the most it has ever done for security reasons — according to local officials in the affected areas. The data, compiled in early September — even before the latest surge in violence in northern Afghanistan —...