“Civil Affairs” has recently been elevated to a branch of the U.S. Army by order of Army Secretary Francis J. Harvey on January 12, 2007.
The role of civil affairs is to support “the interaction of military forces with the civilian populace [in or around the battlefield] to facilitate military operations and consolidate operational objectives.”
According to an Army manual on civil affairs operations (pdf), “A supportive civilian population can provide resources and information that facilitate friendly operations. It can also provide a positive climate for the military and diplomatic activity a nation pursues to achieve foreign policy objectives.”
Conversely, “A hostile civilian population threatens the immediate operations of deployed friendly forces and can often undermine public support at home for the policy objectives of the United States and its allies. When executed properly, civil-military operations can reduce friction between the civilian population and the military force.”
The Army manual has not been approved for public release, but a copy was obtained by Secrecy News.
See “Civil Affairs Operations,” U.S. Army Field Manual FM 3-05.40, September 2006 (184 pages, 4 MB PDF).