Guerrilla
In the 1960s, the Marxist revolutionary Che Guevara developed the foco (Spanish: foquismo) theory of revolution in his book Guerrilla Warfare, based on his experiences during the 1959 Cuban Revolution. This theory was later formalized as "focal-ism" by Régis Debray. Its central principle is that vanguardism by cadres of small, fast-moving paramilitary groups can provide a focus for popular discontent against a sitting regime, and thereby lead a general insurrection. Although the original approach was to mobilize and launch attacks from rural areas, many foco ideas were adapted into urban guerrilla warfare movements.

Strategy, tactics and methods: 

Strategy: Guerrilla warfare is a type of asymmetric warfare: competition between opponents of unequal strength. It is also a type of irregular warfare: that is, it aims not simply to defeat an invading enemy, but to win popular support and political influence, to the enemy's cost. Accordingly, guerrilla strategy aims to magnify the impact of a small, mobile force on a larger, more cumbersome one. If successful, guerrillas weaken their enemy by attrition, eventually forcing them to withdraw.

Tactics: Tactically, guerrillas usually avoid confrontation with large units and formations of enemy troops but seek and attack small groups of enemy personnel and resources to gradually deplete the opposing force while minimizing their own losses. The guerrilla prizes mobility, secrecy, and surprise, organizing in small units and taking advantage of terrain that is difficult for larger units to use. For example, Mao Zedong summarized basic guerrilla tactics at the beginning of the Chinese Civil War as:"The enemy advances, we retreat; the enemy camps, we harass; the enemy tires, we attack; the enemy retreats, we pursue." At least one author credits the ancient Chinese work The Art of War with inspiring Mao's tactics. In the 20th century, other communist leaders, including North Vietnamese Ho Chi Minh, often used and developed guerrilla warfare tactics, which provided a model for their use elsewhere, leading to the Cuban "foco" theory and the anti-Soviet Mujahadeen in Afghanistan.

Unconventional methods: Guerrilla groups may use improvised explosive devices and logistical support by the local population. The opposing army may come at last to suspect all civilians as potential guerrilla backers. The guerrillas might get political support from foreign backers and many guerrilla groups are adept at public persuasion through propaganda and use of force. Some guerrilla movements today also rely heavily on children as combatants, scouts, porters, spies, informants, and in other roles. Many governments and states also recruit children within their armed forces.

Comparison of guerrilla warfare and terrorism: No commonly accepted definition of "terrorism" has attained clear consensus. The term "terrorism" is often used as political propaganda by belligerents (most often by governments in power) to denounce opponents whose status as terrorists is disputed.
While the primary concern of guerrillas is the enemy's active military units, actual terrorists largely are concerned with non-military agents and target mostly civilians.

See also: 

Notes: 

References: Asprey, Robert Brown (2023). "guerrilla warfare". Entry within britannica.
Boeke, Sergei (2019). "Al-Qaeda in the Islamic Maghreb". International Relations. Oxford University Press. doi:10.1093/obo/9780199743292-0267. ISBN 978-0-19-974329-2. Retrieved 17 July 2021.
Boot, Max (2013). Invisible Armies: An Epic History of Guerrilla Warfare from Ancient Times to the Present. Liveright. pp. 10–11, 55. ISBN 978-0-87140-424-4.
Chamberlin, Paul Thomas (2015). The global offensive : the United States, the Palestine Liberation Organization, and the making of the post-cold war order. Oxford University Press. ISBN 978-0-19-021782-2. OCLC 907783262.
Child Soldiers International (2012). "Louder than words: An agenda for action to end state use of child soldiers". Archived from the original on 8 March 2019. Retrieved 19 January 2018.
Child Soldiers International (2016). "A law unto themselves? Confronting the recruitment of children by armed groups". Archived from the original on 8 March 2019. Retrieved 19 January 2018.
Creveld, Martin van (2000). "Technology and War II:Postmodern War?". In Charles Townshend (ed.). The Oxford History of Modern War. New York, USA: Oxford University Press. pp. 356–358. ISBN 978-0-19-285373-8.
Dennis, George (1985). Three Byzantine Military Treatises. Washington, D.C.: Dumbarton Oaks. p. 147.
Detsch, J (2017). "Pentagon braces for Islamic State insurgency after Mosul". Al-Monitor. Archived from the original on 12 July 2017. Retrieved 24 January 2018.
Drew, Allison (2015). "Visions of liberation: the Algerian war of independence and its South African reverberations". Review of African Political Economy. 42 (143): 22–43. doi:10.1080/03056244.2014.1000288. hdl:10.1080/03056244.2014.1000288. ISSN 0305-6244. S2CID 144545186.
Duff, James Grant (2014). The History Of The Mahrattas. Pickle Partners Publishing. p. 376. ISBN 9781782892335.
Ellis, Joseph J. (2005). His Excellency : George Washington. New York: Vintage Books. pp. 92–109. ISBN 9781400032532 – via Internet Archive.
Emmerson, B (2016). "Report of the Special Rapporteur on the promotion and protection of human rights and fundamental freedoms while countering terrorism" (PDF). www.un.org. Retrieved 24 January 2018.
etymonline (2023). "guerrilla". Origin and meaning of guerrilla by Online Etymology Dictionary. Retrieved 14 July 2023.
Ferriter, Diarmaid (2020). "Diarmaid Ferriter: Bloody Sunday 1920 changed British attitudes to Ireland". The Irish Times.
Guevara, Ernesto Che (2006). Guerrilla Warfare – via Internet Archive.
Halibozek, Edward P.; Jones, Andy; Kovacich, Gerald L. (2008). The corporate security professional's handbook on terrorism (illustrated ed.). Elsevier (Butterworth-Heinemann). pp. 4–5. ISBN 978-0-7506-8257-2. Retrieved 17 December 2016.
Hanhimäki, Jussi M.; Blumenau, Bernhard; Rapaport, David (2013). "The Four Waves of Modern Terrorism" (PDF). An International History of Terrorism: Western and Non-Western Experiences. Routledge. pp. 46–73. ISBN 9780415635417. Archived from the original (PDF) on 21 February 2014.
historyireland (2003). "Bloody Sunday 1920: new evidence".
Hooper, Nicholas; Bennett, Matthew (1996). Cambridge illustrated atlas, warfare : the Middle Ages, 768-1487. Cambridge University Press. ISBN 978-0-521-44049-3 – via Internet Archive.
Horne, Alistair (2022). "A Savage War of Peace: Algeria 1954–1962. Rev. ed". The SHAFR Guide Online. doi:10.1163/2468-1733_shafr_sim220070002. Retrieved 17 July 2023.
islamicus (2023). "ABD EL-KRIM". Islamicus. Archived from the original on 14 June 2023.
Keeley, Lawrence H. (1997). War Before Civilization. Oxford University Press.
Kruijt, Dirk; Tristán, Eduardo Rey; Álvarez, Alberto Martín (2019). Latin American Guerrilla Movements: Origins, Evolution, Outcomes. Routledge. ISBN 9780429534270.
Laqueur, Walter (1977). Guerrilla : a historical and critical study. Weidenfeld and Nicolson. ISBN 9780297771845 – via Internet archive.
Lenin, V. I. (1906). "Guerrilla Warfare". Archived from the original on 11 May 2023 – via Internet archive.
Leonard, Thomas M. (1989). Encyclopedia of the developing world.
Mao, Zedong (1965). Selected Works: A Single Spark Can Start a Prairie Fire. Vol. I. Foreign Languages Press – via Internet Archive.