NATO AWACS aircraft assisted in patrolling the skies over the United States after "9-11"
The Balkans remained an important area of interest under the next SACEUR, General Joseph W. Ralston, who took up his duties in May 2000 as only the second Air Force Officer to serve as SACEUR. In Kosovo the size of NATO's Kosovo Force (KFOR) gradually declined as stability was restored, but in the neighbouring former Yugoslav Republic of Macedonia (FYROM)
ethnic unrest followed by an internationally-brokered cease-fire led to a new NATO Balkans mission in the summer of 2001 as NATO troops arrived to receive the weapons being turned in by the National Liberation Front. A small NATO force then remained to provide support to international monitors and subsequently to provide advice and assistance to the government in restoring stability. The NATO mission in FYROM successfully concluded in April 2003, when the European Union took over this responsibility.
The pace and breadth of NATO operations increased sharply in the aftermath of the terrorist attack on the United States on 11 September 2001. The following day NATO invoked Article 5 of the North Atlantic Treaty, which states that an armed attack against one or more of the Allies in Europe or North America shall be considered an attack against them all.
A concrete example of NATO assistance came with Operation EAGLE ASSIST in October 2001, when NATO Airborne Early Warning aircraft began assisting in monitoring the skies over North America. Between October 2001 and May 2002, 830 NATO NAEWF crew members flew more than 4,300 hours and over 360 operational sorties over the United States. An additional NATO response to the threat of terrorism began in late October, when a NATO naval operation – Operation ACTIVE ENDEAVOUR – began in the Eastern Mediterranean and subsequently expanded to provide safe passage for Allied shipping in the Straits of Gibraltar and operations throughout the Mediterranean.
During this period the United States along with local Afghan forces succeeded in toppling the Taliban regime in Afghanistan, which had previously provided a safe haven for the Al Qaeda terrorist organisation. Afterward an International Security and Assistance Force (ISAF) was established in December 2001 to provide assistance in restoring stability and self-governance in the country, but initially this force was not under NATO command.
In November 2002, shortly before General Ralston stepped down as SACEUR, the leaders of the NATO member nations met at the Prague Summit and decided upon a wide-ranging and ambitious transformation of the Alliance. In terms of structures, there would in the future be only one command with responsibility for all NATO operations – Allied Command Operations with its headquarters at SHAPE – while the new Allied Command Transformation headquartered at Norfolk, Virginia, in the United States, would be responsible for developing the doctrines and tools that NATO would need in the 21st Century.
The Prague Summit also decided to give the Alliance new capabilities, the most important of which was new NATO Response Force (NRF) capable of providing a rapid response to a looming or actual crisis. The process of manning and training this new force occurred under the next SACEUR, General James L. Jones, who took up his post in January 2003 as the first Marine Corps officer to serve as SACEUR. During the next 3¾ years General Jones oversaw the development of the NRF through force generation by the nations and increasingly complex training exercises. In one of his final acts as SACEUR, General Jones declared in November 2006 that the NRF had attained Full Operational Capability.