Afghanistan has been in a near perpetual state of war for the last 300 years or so. In fact, the years when the country has been at peace are dwarfed by the number of years when the country has been at war. The tribal split between the Pashtuns and the Tajiks has been the casus belli for most of these conflicts and the various 'western' interventions have traditionally exploited these divisions.
Unfortunately, I can see no reason why peace will return to Afghanistan once the west pulls out.