The Wealth of Nations by Part 5 Chapter 1 Page 43

As arts and industry advanced, however, the authority of the chieftains gradually decayed, and the great body of the people had less time to spare for military exercises. Both the discipline and the exercise of the feudal militia, therefore, went gradually to ruin, and standing armies were gradually introduced to supply the place of it. When the expedient of a standing army, besides, had once been adopted by one civilised nation, it became necessary that all its neighbours should follow their example. They soon found that their safety depended upon their doing so, and that their own militia was altogether incapable of resisting the attack of such an army.

The soldiers of a standing army, though they may never have seen an enemy, yet have frequently appeared to possess all the courage of veteran troops and the very moment