U.S. Army General John W. "Mick" Nicholson has taken command of U.S. and NATO forces in Afghanistan, inheriting America's longest war and a vicious insurgency.

Nicholson, 58, took over Wednesday from U.S. Army General John F. Campbell, who oversaw the end of the international combat mission in 2014 and an escalation in the Taliban's war against Kabul.

In a ceremony at the headquarters of the U.S.-NATO Resolute Support mission in Kabul, Nicholson thanked NATO representatives for standing by the U.S. after the September 11, 2001 attacks on "the homeland."

To the Taliban, he said: "I know you. You have brought only hardship and suffering to the Afghan people."

Nicholson served in Afghanistan three times between 2006 and 2012. He takes command of around 13,000 international troops, including 9,800 Americans.