While most Americans agreed when President George W. Bush said that the terrorist attacks of September 11 ushered in a new era of warfare, the US armed forces and military medicine had already been adopting new rules of engagement.
Since the collapse of the Soviet Union and the end of the Cold War, the US Department of Defense has moved away from the philosophy of conventional warfare against sovereign states that involved thousands of troops stationed on miles-long fronts. The new philosophy is meant to support warfare that can occur in multiple settings, featuring smaller fighting units against terrorists or rogue states. The military has already seen such action in Bosnia, Kosovo, and Somalia and is now applying it in Afghanistan.
Mitka M. US Military Medicine Moves to Meet Current Challenge. JAMA. 2001;286(20):2532-2533. doi:10.1001/jama.286.20.2532-JMN1128-2-1