A more thorough explanation:

Definition: National defense refers to all the actions taken by a country to protect itself from its enemies. This includes the military establishment as well as the protection of a country's values and ideals.

Examples: A country may take various measures to defend itself, such as building a strong military, creating alliances with other countries, and developing advanced technology for defense purposes. In times of war or national emergency, a country may also implement emergency measures to protect its citizens and resources.

Explanation: National defense is essential for a country's security and sovereignty. The examples illustrate how a country can take different measures to protect itself from external threats. For instance, building a strong military can deter potential aggressors from attacking a country. Similarly, alliances with other countries can provide additional support and resources in times of need. Emergency measures, such as curfews or evacuations, can help protect citizens and resources during times of crisis.