Foreign internal defense (FID) is a term used by the military in several countries, including the United States, France, and the United Kingdom, to describe an integrated, or multi-country approach to combating actual or threatened insurgency in a foreign state. This foreign state is known as the Host Nation (HN) under the US (and generally accepted NATO) doctrine. The term counter-insurgency is commonly used for FID.
FID involves military deployment of counter-insurgency specialists. According to the US doctrinal manual, Joint Publication 3-22: Foreign Internal Defense (FID), these specialists occasionally get involved with the actual fighting. This doctrine calls for a close working relationship between the Host Nation government and security specialists, which could include diplomatic, information, intelligence, military, economic, and other specialties. A successful FID action is one that leads to the suppression of actual violence. If combat operations are required, Host Nation security forces take the lead. FID is tasked with external support and training where required.
Formally, FID is defined as "Participation by civilian and military agencies of a government in any of the action programs taken by another government or other designated organization to free and protect its society from subversion, lawlessness, and insurgency."
FID is a multinational and interagency effort that requires the integration and synchronization of many different factions of national power.
The joint forces that make up the FID effort, support other instruments of national power as well,(diplomatic, information/intelligence, economic, etc.) to protect and enhance Host Nation security interests. These actions may include:
Military engagement,
Security cooperation (SC), and
Deterrence
Within this range of military operations, nation assistance (NA) is civil or military assistance (other than foreign humanitarian assistance [FHA]) rendered to a nation by US forces within that nation's territory during peacetime, crises or emergencies, or war, based on agreements mutually concluded between the United States and that nation.