Militias

A militia /mᵻˈlɪʃə/ is generally an army or some other type of fighting unit that is composed of non-professional fighters, citizens of a nation or subjects of a state or government who can be called upon to enter a combat situation, as opposed to a professional force of regular, full-time military personnel, or historically, members of the warrior nobility class (e.g., knights or samurai). Unable to hold their own against properly trained and equipped professional forces, it is common for militias to engage in guerrilla warfare or defense instead of being used in open attacks and offensive actions.

With the emergence of professional forces (in the form of mercenaries whose livelihood was military service) during the Renaissance, Western European militias wilted; later however, they would be revived as part of Florentine civic humanism, which held that professional militaries were a result of corruption, and admired the Roman model. The civic humanist ideal of the militia was spread through Europe by the writings of Niccolò Machiavelli (According to Hörnqvist, The Prince, ch. 12 and 13, Discourses on Livy, and The Art of War.)

Beginning in the late 20th century, some militias (in particular officially recognized and sanctioned militias of a government) act as professional forces, while still being "part-time" or "on-call" organizations. For instance, the members of some U.S. Army National Guard units are considered professional soldiers, as they are trained to maintain the same standards as their "full-time" (active duty) counterparts.

...
Wikipedia