Military service in its simplest sense, is service by an inividual or group in an army or other military organization, whether as a chosen job or as a result of an involuntary draft (conscription). Some nations (e.g. Israel) require a specific amount of military service from each and every one of its citizens (except for special cases such as mental illness or religious beliefs). 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.