Asymmetric warfare (or asymmetric engagement) is a type of war between belligerents whose relative military power, strategy, or tactics differ significantly. This type of warfare often, but not necessarily, involves insurgents or resistance movement militias who may have the status of unlawful combatants against a standing army.
Asymmetrical warfare can also describe a conflict in which belligerents' resources are uneven, and consequently, they both may attempt to exploit each other's relative weaknesses. Such struggles often involve unconventional warfare, with the weaker side attempting to use strategy to offset deficiencies in the quantity or quality of their forces and equipment. Such strategies may not necessarily be militarized. This is in contrast to symmetrical warfare, where two powers have comparable military power, resources, and rely on similar tactics.
Asymmetric warfare is a form of irregular warfare – conflicts in which enemy combatants are not regular military forces of nation-states. The term is frequently used to describe what is also called guerrilla warfare, insurgency, counterinsurgency, rebellion, terrorism, and counterterrorism.
The popularity of the term dates from Andrew J. R. Mack's 1975 article "Why Big Nations Lose Small Wars" in World Politics, in which "asymmetric" referred simply to a significant disparity in power between opposing actors in a conflict. "Power," in this sense, is broadly understood to mean material power, such as a large army, sophisticated weapons, an advanced economy, and so on. Mack's analysis was largely ignored in its day, but the end of the Cold War sparked renewed interest among academics. By the late 1990s, a new research building off Mack's works was beginning to mature; after 2004, the U.S. military began once again to prioritize responding to challenges presented by asymmetric warfare.
Since 2004, the discussion of asymmetric warfare has been complicated by the tendency of academic and military officials to use the term in different ways, as well as by its close association with guerrilla warfare, insurgency, terrorism, counterinsurgency, and counterterrorism.