Gen. Stanley McChrystal, a former top special operations commander, took charge of nearly 90,000 U.S. and NATO troops in Afghanistan on Monday, telling them they must protect Afghan civilians from all kinds of violence.

McChrystal takes over the Afghan campaign at a critical moment: violence, troop levels and U.S. military deaths have all hit record highs, and President Hamid Karzai has increased pressure on U.S. forces to prevent civilian deaths.

Seeking to shake up the direction of the war, Defense Secretary Robert Gates sent McChrystal to lead the 42-nation effort in Kabul in the middle of U.S. Gen. David McKiernan’s two-year assignment, effectively ending the career of a four-star general whom McChrystal called a “fellow soldier and friend.”

McChrystal is expected to take a more unconventional approach to the increasingly violent campaign in Afghanistan, relying on decades of experience with special operators — elite military units like Navy SEALs and Army’s Delta Force that carry out dangerous and secretive missions.