The armed forces of a country are its government-sponsored defense, fighting forces, and organizations. They exist to further the foreign and domestic policies of their governing body, and to defend that body and the nation it represents from external and internal aggressors. In some countries paramilitary forces are included in a nation's armed forces. Armed force is the use of armed forces to achieve political objectives.
The study of the use of armed forces is called military science. Broadly speaking, this involves considering offense and defense at three "levels": strategy, operational art, and tactics. All three levels study the application of the use of force in order to achieve a desired objective.