In some instances, national service is compulsory, and citizens living abroad can be called back to their country of origin to complete it.
Compulsory military service typically requires all citizens to enroll for one or two years, usually at age 18 (later for university-level students).
Voluntary national service may require only three months of basic military training.
In the United States, voluntary enrollments at the Peace Corps and AmeriCorps are also known as national service.
Around 100 AD, Plutarch quoted an early case for national service made by a Roman general sometime around the 5th century BC:With the politic design of preventing intestine broils by employment abroad, and in the hope that when rich as well as poor, plebeians and patricians, should be mingled again in the same army and in the same camp, and engage in one common service for the public, it would mutually dispose them to reconciliation and friendship.