While most warlords have power vested in them through traditional tribal customs, some hold formal regional government positions, but in both cases cooperation with the central government remains voluntary and reliant on incentives. Beginning in 2008, as it became increasingly evident that the central government in Kabul was incapable of extending its power and control to much of the country, the US military and diplomatic corps began exploring the option of engaging ethnic tribal warlords in negotiations, a strategy that continued through the Obama administration.