We have already noted how the breaking up of the unity of Christendom by the development of state churches was but a phase of the operation of new forces at work, at the beginning of the modern era, which were moulding men's thoughts and emotions along national lines. In their religious aspect, these gave rise to the post-Reformation churches, and in their political aspect, to the growth of the modern state. They were equally powerful in the economic field; and the so-called Mercantile Theory, which was the ground of the imperial theories of the time, was but the reasoned expression of this nationalizing of the economic life of the peoples. In the Middle Ages, the life of the individual, in its various relations, had been decentralized. In his political allegiance he had looked one way, in his religious another, and in his economic still another. The growing strength of the feeling of nationality was gradually drawing all toward a common centre. The balance of trade, which forms one of the essential features of the Mercantile Theory, was not a new conception. It was, however, of great practical influence upon economic doctrine and state policies when applied to the nations. After speaking of how a merchant balances his private books, and how the head of a family looks after his estate, an early writer goes on to say that “the Royall Merchant, the Regall Father of that great family of a Kingdom, if He will know the Estate of his Kingdome, Hee will compare the Gaine thereof with the Expense; that is, the Native Commodities issued and sent out, with the Forraine Commodities received in; and if it appeare that the Forraine Commodities doe exceed the Native, either he must increase the Native, or lessen the Forraine, or else looke for nothing else, but the Decay of Trade and therein the losse of his Revenue, and Impoverishing of his People.”[718] Footnote 718: E. M[isselden], _The Circle of Commerce or the Ballance of Trade_ (London, 1623), p. 131.