Guerrilla warfare
Guerrilla is a term invented in Spain to describe the tactics used to resist the French regime instituted by Napoleon Bonaparte (one should however remember, that the tactics themselves were known and used even centuries earlier). It means "little war". It is based in small, mobile and flexible combat groups called cells, without a front line.
Guerrilla tactics are based on ambush and sabotage, and their ultimate objective is usually to destabilize the government through long, low-intensity confrontation. It can be quite successful against an unpopular foreign regime, in which the guerrilla army increases the cost of maintaining an occupation or colonial presence above what the foreign power is willing to bear. Examples of successful guerrilla warfare include Indonesia, Angola, Mozambique and Algeria. However, it has generally been unsuccessful against native regimes, which have nowhere to retreat to. The rare examples of successful guerrilla warfare against a native regime include Cuba and China. More common are the unsuccessful examples which include Malaysia, Bolivia, Argentina, and the Philippines.
Guerillas are usually characterised as terrorists by their opponents, however guerillas in wars against foreign powers do not principally direct their attacks at civilians, as they desire to extract as much support as possible from the population as part of their tactics. An exception is in civil wars, where both guerilla groups and organized armies have been known to commit atrocities against the civilian population.
Guerrillas usually control rural areas with lots of places to hide, such as forests and mountains. Guerrillas rely on a friendly population to provide supply and intelligence.
Maoist theory of people's war divides warfare into three phases. In the first phase, the guerrillas gain the support of the population. In the second phase, involved escalating attacks which become more and more conventional. In the third phase, conventional means to overthrow the government.
In the 1960s and 1970s, Latin America had a number of urban guerrilla movements whose strategy was to destabilize democratic regimes and provoke a counter-reaction by the military. The theory was that a harsh military regime would oppress the middle classes who would then support the guerrillas create a popular uprising. Unfortunately, while these movements did destabilize governments, such as Argentina and Uruguay, to the point of military intervention, the military generally then proceeded to wipe out the guerrilla movements, often committing extreme human rights violations in the process.
The Vietnam War is commonly thought of as a guerrilla war in the United States. However this is misleading simplification of a more complex situation which followed the pattern outlined by Maoist theory. It is the case the Viet Cong used guerrilla tactics in the early phases of the war. However, by 1965 when American involvement escalated, the Viet Cong where in the process of being replaced by regular units of the North Vietnamese Army. These units were organized along traditional military lines, were supplied via the Ho Chi Minh trail rather than living off the land, and had access to and in general used weapons such as artillery, which are not normally used by guerrilla forces.
Over time, more of the fighting was conducted by the North Vietnamese Army and the character of the war become increasingly conventional. The final offensive into South Vietnam in 1975 was a completely conventional military operation with no elements of guerrilla warfare.