The re-emergence of the Islamic Talilban movement in the recent years as a fighting force in Afghanistan and a major threat to the government.
Even Pakistan is being threatned by them and they control the areas in the north-west and are blamed for a wave of suicide attacks.
Taliban has emerged in the early 1990s in northern Pakistan when the Soviet troops have writhdrawn from Afghanistan.
A predominantly Pashtun movement, the Talibans became prominent in Afghanistan during 1994.
Its belived that they first appeared in religious seminars - mostly for money from Saudi Arabia which preached hard line form of Sunni Islam.
The Taliban's promise - in Pashtun areas straddling Pakistan and Afghanistan - was to restore peace and security and enforce their own austere version of Sharia, or Islamic law, once in power.
Despite ever higher numbers of foreign troops, the Taliban have steadily extended their influence, rendering vast tracts of Afghanistan insecure.
Their retreat earlier this decade enabled them to limit their human and material losses and return with a vengeance.