The first duty of the sovereign, that of protecting the society from the violence and invasion of other independent societies, can be performed only by means of a military force. But the expense both of preparing this military force in time of peace, and of employing it in time of war, is very different in the different states of society, in the different periods of improvement.
Adam Smith, "The Wealth of Nations 5", I.1.1
Discount Link: http://bit.ly/wr-discount