The loss of such a large portion of British America, at the time Britain's most populous overseas possession, is seen by some historians as the event defining the transition between the "first" and "second" empires, in which Britain shifted its attention away from the Americas to Asia, the Pacific and later Africa. Adam Smith's Wealth of Nations, published in 1776, had argued that colonies were redundant, and that free trade should replace the old mercantilist policies that had characterised the first period of colonial expansion, dating back to the protectionism of Spain and Portugal. The growth of trade between the newly independent United States and Britain after 1783 seemed to confirm Smith's view that political control was not necessary for economic success.