National security is the requirement to maintain the survival of the state through the use of economic power, diplomacy, power projection and political power.
The concept developed mostly in the United States after World War II.
Initially focusing on military might, it now encompasses a broad range of facets, all of which impinge on the non military or economic security of the nation and the values espoused by the national society.
Accordingly, in order to possess national security, a nation needs to possess economic security, energy security, environmental security, etc.
Security threats involve not only conventional foes such as other nation-states but also non-state actors such as violent non-state actors, narcotic cartels, multinational corporations and non-governmental organisations; some authorities include natural disasters and events causing severe environmental damage in this category.
Measures taken to ensure national security include:
using diplomacy to rally allies and isolate threats
marshalling economic power to facilitate or compel cooperation
maintaining effective armed forces
implementing civil defense and emergency preparedness measures (including anti-terrorism legislation)
ensuring the resilience and redundancy of critical infrastructure
using intelligence services to detect and defeat or avoid threats and espionage, and to protect classified information
using counterintelligence services or secret police to protect the nation from internal threats