What was the use and object of the Empire? In brief, according to the theory and practice then in force, the end of empire was the profit which comes from trade; the means was the political subordination of the colonies to prevent interference with this profit; and the debit entry set against this profit was the cost of the diplomacy, the armaments, and the wars required to hold the overseas possessions against other powers. The policy was still that which had been set forth in the preamble of the Navigation Act of 1663, ensuring the mother country the sole right to sell European wares in its colonies: "the maintaining a greater correspondence and kindness between them [the subjects at home and those in the plantations] and keeping them in a firmer dependence upon it [the mother country], and rendering them yet more beneficial and advantageous unto it in the further Imployment and Encrease of English Shipping and Seamen, and vent of English Woollen and other Manufactures and Commodities rendering the Navigation to and from the same more safe and cheape, and makeing this Kingdom a Staple not only of the Commodities of those Plantations but also of the Commodities of other countries and places for the supplying of them, and it being the usage of other Nations to keep their [plantation] Trade to themselves." Adam Smith had raised a doubt as to the wisdom of the end. The American Revolution had raised a doubt as to the wisdom of the means. Yet, with significant changes, the old colonial system lasted for full two generations after 1776.