Military service is service by an individual or group in an army or other militia, whether as a chosen job or as a result of an involuntary draft (conscription). Some nations (e.g., Mexico) require a specific amount of military service from every citizen (except for special cases, such as physical or mental disorders or religious beliefs, and most countries that have conscription only conscript men). A nation with a fully volunteer military does not normally require mandatory military service from its citizens, unless it is faced with a recruitment crisis during a time of war.