The Wealth of Nations by Part 3 Chapter 3 Page 10

revenue which was, perhaps, of all others the most likely to be improved by the natural course of things, without either expense or attention of their own: and that they should, besides, have in this manner voluntarily erected a sort of independent republics in the heart of their own dominions.

In order to understand this, it must be remembered that in those days the sovereign of perhaps no country in Europe was able to protect, through the whole extent of his dominions, the weaker part of his subjects from the oppression of the great lords. Those whom the law could not protect, and who were not strong enough to defend themselves, were obliged either to have recourse to the protection of some great lord, and in order to obtain it to become either his slaves or vassals; or to enter into a league of mutual defence for the