“A government is the means of placing the retaliatory use of physical force under objective control—i.e., under objectively defined laws.” — AYN RAND
Man’s state in nature, where every man is allowed complete discretion in the retaliatory use of force, according to the laws of the jungle, is anarchy — perpetual civil war and gang warfare. If there were no legal agency to carry out such a task, each man would be forced to carry out retaliation at his discretion. Writes Ayn Rand on the need for government:
“If a society left the retaliatory use of force in the hands of individual citizens, it would degenerate into mob rule, lynch law and an endless series of bloody private feuds or vendettas. If physical force is to be barred from social relationships, men need an institution charged with the task of protecting their rights under an objective code of rules. This is the task of a government—of a proper government—its basic task, its only moral justification and the reason why men do need a government. 
Under capitalism, a proper government’s fundamental responsibility is to protect the rights of the individual, by banning the initiation of physical force, thus making all relations between men voluntary, i.e., free from the threat of violence and fraud.
 Ayn Rand, The Nature of Government