Counterinsurgency strategy in Iraq changed significantly under the command of General Petraeus since the 2007 troop surge began.[57] The newer approach attempted to win the hearts and minds of the Iraqi people through building relationships, preventing civilian casualties and compromising with and even hiring some former enemies.[58] The new strategy was population-centric in that it focused in protecting the population rather than killing insurgents.[59] In implementing this strategy, Petraeus used experience gained while commanding the 101st Airborne Division in Mosul in 2003. He also explained these ideas extensively in Field Manual 3-24: Counterinsurgency,[60] which he assisted in the writing of while serving as the Commanding General of Fort Leavenworth, Kansas, and the US Army Combined Arms Center (CAC) located there.