Foreign internal defense

Foreign internal defense (FID) is a term used by a number of Western militaries, including the United States, France and the United Kingdom, to describe an approach to combating actual or threatened insurgency in a foreign state called the Host Nation (HN). The term counter-insurgency is more commonly used worldwide than FID. FID involves military deployment of counter-insurgency specialists. According to the US doctrinal manual, Joint Publication 3-07.1: Foreign Internal Defense (FID), those specialists preferably do not themselves fight the insurgents. Doctrine calls for a close working relationship between the HN government and military with outside military, diplomatic, economic, and other specialists. The most successful FID actions prevent actual violence, although that is rarely possible. When combat is needed, it is best done by HN personnel with appropriate external support, the external support preferably being in a noncombat support and training role alone.

United States
US Army Special Forces' original mission was to train and lead guerrillas in a nation occupied by another: "[US Special Forces provided] advisory personnel and mobile training teams to advise, train and provide operational assistance for paramilitary forces." The most likely case, at the time Special Forces were created, would be to lead resistance groups in European countries overrun by the expected Soviet Bloc attack. Over time, the term guerrilla warfare, especially led by Americans, fell into disfavor, and unconventional warfare took its place.

Unfortunately, human rights violations tend to be common during insurgencies. Western powers are under considerable pressure to be sure to include human rights training in the overall assistance to HN personnel, although the results vary. Part of the challenge comes when HN personnel go into combat without FID advisors to monitor their conduct. However in the El Salvador case, the US-trained Salvadoran army's Atlacatl Battalion's intent to commit mass killing in 1981 at El Mozote, Morazan province, with the result of 900+ civilians killed, was known to at least one US military advisor monitoring the battalion's activities, according to US military advisor veteran and historian from that era, Greg Walker. No formal US government investigation of that advisor's action or inaction to deter or facilitate the massacre apparently ever has been carried out.