While in theory the term refers exclusively to hostility against combatants or militants, in reality the distinctions between "combatant" and "civilian" are often beyond the means of military intelligence to make discernments. As such, known counter-insurgency operations have often rested on a confused, relativistic, or otherwise situational distinction between combatant and civilians, and use of the terms "insurgent" and "counter-insurgent" themselves have sometimes hinged on a subjective perception of the government's legitimacy. As such, the term "counter-insurgency" is somewhat cognate with "suppression" of rebellion.
To understand counter-insurgency, one must understand insurgency. See models of insurgency to understand the dynamics of revolutionary warfare. Insurgents capitalize on societal problems, often called gaps; counter-insurgency addresses closing the gaps. When the gaps are wide, they create a sea of discontent, of which Mao wrote "the guerilla must swim in the people as the fish swims in the sea."
William B. Caldwell wrote:
The law of armed conflict requires that, to use force, "combatants" must distinguish individuals presenting a threat from innocent civilians. This basic principle is accepted by all disciplined militaries. In the counterinsurgency, disciplined application of force is even more critical because our enemies camouflage themselves in the civilian population. Our success in Iraq depends on our ability to treat the civilian population with humanity and dignity, even as we remain ready to immediately defend ourselves or Iraqi civilians when a threat is detected.
A somewhat similar strategy was used extensively by US forces in South Vietnam, initially by forcing the rural population into fenced camps, referred to as Strategic Hamlets, and later by declaring the previous areas as free-fire zones to remove the rest from their villages and farms. Widespread use was made of Agent Orange, sprayed from airplanes, to destroy crops that might possibly have provided resources for Viet Cong and North Vietnamese troops and their human support base. These measures proved ineffective, as the Viet Cong often relocated activists and sympathizers inside the new communities. In any event, the Vietnam War was only partly a counter-insurgency campaign, as it also involved conventional combat between US forces and the North Vietnamese. After the US withdrew from Vietnam in 1973, the North Vietnamese rebuilt their forces and conducted a conventional invasion of the South two years later.
The majority of counter-insurgency efforts by major Western powers in the last century have been spectacularly unsuccessful. This may be attributed to a number of causes. First, as Sir Basil Henry Liddell Hart pointed out in the Insurgency addendum to the second version of his book Strategy: The Indirect Approach, a popular insurgency has an inherent advantage over any occupying force. He showed as a prime example the French occupation of Spain during the Napoleonic wars. Whenever Spanish forces managed to constitute themselves into a regular fighting force, the superior French forces beat them every time. However, once dispersed and decentralized, the irregular nature of the rebel campaigns proved a decisive counter to French superiority on the battlefield. Napoleon's army had no means of effectively combatting the rebels, and in the end their strength and morale were so sapped that when Wellington was finally able to challenge French forces in the field, the French had almost no choice but to abandon the situation.
Hart also points to the experiences of T. E. Lawrence and the Arab Revolt during World War I as another example of the power of the rebel/insurgent. Though the Ottomans often had advantages in manpower of more than 100 to 1, the Arabs' ability to materialize out of the desert, strike, and disappear again often left the Turks reeling and paralyzed, creating an opportunity for regular British forces to sweep in and finish the Turkish forces off.
In both the preceding cases, the insurgents and rebel fighters were working in conjunction with or in a manner complementary to regular forces. Such was also the case with the French Resistance during World War II and the National Liberation Front during the Vietnam War. The strategy in these cases is for the irregular combatant to weaken and destabilize the enemy to such a degree that victory is easy or assured for the regular forces. However, in many modern rebellions, one does not see rebel fighters working in conjunction with regular forces. Rather, they are home-grown militias or imported fighters who have no unified goals or objectives save to expel the occupier. In these cases, such as the Israeli occupation of Lebanon, which ended in 2000, and the current Iraqi insurgency, the goal of the insurgent is not to defeat the occupying military force; that is almost always an impossible task given the disparity in resources. Rather, they seek through a constant campaign of sneak attacks to inflict continuous casualties upon their superior enemy forces and thereby over time demoralize the occupying forces and erode political support for the occupation in the homeland of the occupying forces. It is a simple strategy of repeated pin-pricks and bleedings that, though small in proportion to the total force strength, sap the will of the occupier to continue the fight.
According to Liddell Hart, there are few effective counter-measures to this strategy. So long as the insurgency maintains popular support, it will retain all of its strategic advantages of mobility, invisibility, and legitimacy in its own eyes and the eyes of the people. So long as this is the situation, an insurgency essentially cannot be defeated by regular forces. The US in Vietnam attempted to neutralize this advantage by simply taking away the civilian population that shielded the insurgents; however, this had the foreseeable effect of alienating the populace and further fueling support for the rebels. In the current operations against insurgents in the "War on Terror", such ruthless tactics are not available to commanders, even if they were effective. Another option in combating an insurgency would be to make the presence of troops so pervasive that there is simply no place left for insurgents to hide, as demonstrated in Franco's conquest of Republican Spain during the Spanish Civil War or the Union occupation of Confederate States with Federal troops following the American Civil War. In each of these cases, enormous amounts of manpower were needed for an extended period of time to quell resistance over almost every square kilometre of territory. In an age of ever shrinking and increasingly computerized armed forces, this option too is precluded from a modern commanders options.
Essentially, then, only one viable option remains. The key to a successful counter-insurgency is the winning-over of the occupied territory's population. If that can be achieved, then the rebellion will be deprived of its supplies, shelter, and, more importantly, its moral legitimacy. Unless the hearts and minds of the public can be separated from the insurgency, the occupation is doomed to fail. In a modern representative democracy, in the face of perceived incessant losses, no conflict will be tolerated by an electorate without significant show of tangible gains. It should be noted that though the United States and its ARVN allies won every single major battle with North Vietnamese forces and their opponents suffered staggering losses (2 million+ casualties), the cost of victory was so high in the opinion of the US public (58,193 U.S. casualties) that it came to see any further possible gains as not worth the troop losses. As long as popular support is on their side, an insurgency can hold out indefinitely, consolidating its control and replenishing its ranks, until the occupiers simply leave.
"Among the most effective means are such population-control measures as vehicle and personnel checkpoints and national identity cards. In Malaya, the requirement to carry an ID card with a photo and thumbprint forced the communists to abandon their original three-phase political-military strategy and caused divisive infighting among their leaders over how to respond to this effective population-control measure."
"However, the initial problem that the British government faced was in finding a suitably coordinated and controlled body that could execute its will. Just who exactly was in charge and who ultimately would make decisions was a problem that would restrict the effectiveness of British counter-insurgency for many years."
While McClintock cites the 1894 Algerian governor, Jules Cambon, as saying "By destroying the administration and local government “we were also suppressing our means of action.” “The result is that we are today confronted by a sort of human dust on which we have no influence and in which movements take place which are unknown to us.“ Cambon's philosophy, however, did not seem to survive into the Algerian War of Independence, (1954-1962).
It occurred to various commanders that soldiers trained to operate as guerrillas would have a strong sense of how to fight guerrillas. Before the partition of French Indochina, French Groupement de Commandos Mixtes Aéroportés (GCMA), led by Roger Trinquier, took on this role, drawing on French experience with the Jedburgh teams. GCMA, operating in Tonkin and Laos under French intelligence, was complemented by Commandos Nord Viêt-Nam in the North. In these missions, the SOF teams lived and fought with the locals. One Laotian, who became an officer, was Vang Pao, who was to become a general in Hmong and Laotian operations in Southeast Asia while the US forces increased their role.
Counter-insurgency requires an extremely capable intelligence infrastructure endowed with human sources and deep cultural knowledge. This contributes to the difficulty that foreign, as opposed to indigenous, powers have in counter-insurgent operations. One of France's most influential theorists was Roger Trinquier. The Modern Warfare counterinsurgency strategy described by Trinquier, who had led anti-communist guerillas in Indochina, was a strong influence on French efforts in Algeria.
Trinquier suggested three principles:
Trinquier's view was that torture had to be extremely focused and limited, but many French officers considered its use corrosive to its own side. There were strong protests among French leaders: the Army’s most decorated officer, General Jacques Pâris de Bollardière, confronted General Jacques Massu, the commander of French forces in the Battle of Algiers, over orders institutionalizing torture, as "an unleashing of deplorable instincts which no longer knew any limits." He issued an open letter condemning the danger to the army of the loss of its moral values "under the fallacious pretext of immediate expediency", and was imprisoned for sixty days.
As some of the French Army protested, other parts increased the intensity of their approach, which led to an attempted military coup against the French Fourth Republic itself. Massu and General Raoul Salan led a 1958 coup in Algiers, demanding a new Republic under Charles de Gaulle. When deGaulle's policies toward Algeria, such as a 1961 referendum on Algerian self-determination, did not meet the expectations of the colonial officers, Salan formed the underground Organisation de l'armée secrète (OAS), a right-wing terrorist group, whose actions included a 1962 assassination attempt against de Gaulle himself.
Established in 1970, the school is considered one of the world's most prestigious anti-terrorist institutions. Soldiers from India and the United States participating at a long exercise in guerrilla warfare in Counter Insurgency and Jungle Warfare School at Vairengte in Mizoram. Today there is a joint effort in which graduate level and high quality education is being given by a joint staff of highly trained special operators at Camp Taji Phoenix Academy and the Counterinsurgency Center For Excellence in Iraq. This facility is used to train the US military training team members (MTT) as well as many Iraqi Officers.
As used by the U.S. Army, counter-insurgency operations include psychological warfare and information warfare, which is waged both by the insurgents and counter-insurgency forces. In the main, the insurgents seek to destroy or erase the political authority of the defending authorities in a population they seek to control, where the counter-insurgent forces seek to protect it and reduce or eliminate the supplanting authority of the insurgents.
The CIA and South Vietnamese security forces conducted the Phoenix Program to neutralize Viet Cong sympathizers, when the Viet Cong were killing teachers, village headmen, and other manifestations of the Saigon government at local level. The USMC's Combined Action Program is another, more successful example of counterinsurgency efforts in Vietnam.
The U.S., British and allied occupation forces and the Iraqi security forces are currently engaging in a counter-insurgency operation against various Iraqi guerrilla groups and supporters of the resistance from outside Iraq who are opposed to the presence of foreign troops and the current Iraqi government.
As the British found in Iraq in the 1920s and in some encounters in the frontier in Pashtunistan, aircraft stripped away many of the advantages that traditional insurgents had enjoyed. It also offered a way of inflicting direct and cost-effective retaliation on the communities that supported the insurgents. Such measures are not so common now, as they are not palatable to the domestic populations of Western nations.
At first (particularly during the Vietnam War) counter-insurgency missions were flown by existing airplanes and helicopters hastily adapted for the role, notably the Douglas A-1 Skyraider. Later, more specialized counter-insurgency (or COIN) aircraft began to appear, such as: