Which small country has the world’s smallest national army by active personnel?

Vatican City has the world’s smallest national army by active personnel: the Swiss Guard.

The Pontifical Swiss Guard protects the pope and key entrances to Vatican City. It was founded in 1506 by Pope Julius II, and its members are Swiss citizens who meet strict requirements involving age, training, faith and military service.

The force is ceremonial as well as operational. Guards wear the famous Renaissance-inspired uniform during public duties, but they also receive modern security training. The Vatican also works with Italy and other agencies for wider security arrangements.

The Swiss Guard is sometimes described as a police force, but its formal role is military protection of the pope and the Apostolic Palace. Vatican City’s Gendarmerie handles internal policing. The guard’s small size changes over time, but its historic identity and mission make it the canonical answer to this question.