Defense services are needed to defend the country, its vital national interests, and values against external and internal (existing or potential) threats of armed aggression. In short, Armed Forces are imperative as the ultimate instrument of National Security. The defense has to do with protecting something or fighting against an opponent, whether it's national defense, a football team's defense, or a defense lawyer. The defense is the opposite of offense. It has to do with defending against all sorts of things: In the military, the defense is about protecting a country from attack. In civil proceedings and criminal prosecutions under the common law, a defendant may raise a defense in an attempt to avoid criminal or civil liability.