What are Two reasons national defense is a public good?

National defense is considered a public good because it is non-excludable and non-rivalrous. This means that once national defense is provided, it protects all citizens regardless of whether they contribute to its funding, and one person's security does not diminish the security available to others. Additionally, the benefits of national defense extend beyond individual citizens to society as a whole, creating a stable environment essential for economic growth and social well-being.