British merchants not satisfied with this monopoly procured a more stringent act in 1663, which provided that no commodity, the growth, product, or manufacture of Europe, should be imported into the colonies, except in English-built ships, sailing from English ports. By this act England became the sole market in which the colonists could purchase the products or manufactures of Europe, nor could they send their own ships for them, unless English-built or bought before October 1, 1662. They were obliged to buy in English markets and import in English vessels.[15] This discouraged ship-building for the European trade in a country full of timber, and compelled the payment of charges and profits to English factors dealing in Continental goods for the American market. By these two acts British merchants had undertaken to monopolize, with certain exceptions, the carrying trade of the colonies and their markets for the sale and the purchase of goods. But avarice was not satisfied. There had grown up a trade, especially profitable to New England, with the Southern colonies which were without shipping. By the act of 1660, foreign and intercolonial trade in certain articles was permitted, with the expectation that it would be limited to necessary local supply. But Boston merchants, shipping to that port tobacco and some other colonial products in excess of the local demand, sent the surplus to Continental Europe, without payment of British or colonial duties, and thus undersold the British trader, who had paid heavy import duties. To suppress this profitable irregularity, it was enacted in 1672 that the enumerated products shipped to other colonies should be first transported to England, and thence to the purchasing colony. The colonial merchants had the option, however, of bringing tobacco, for instance, from Virginia direct to Massachusetts, first paying an export duty equivalent to the English import duty.[16] These enactments subjected colonial interests to those of British ship-owners and merchants; and as they had been thus duly protected, the manufacturers in turn claimed similar protection by statutes which should prevent the colonists from setting up competing manufactories.[17] How could there have been any difference of opinion among the colonists respecting such statutes? A general answer is, that the colonial system, which regarded the colonies as feeders for the navigation, trade, and manufactures of the parent state, was the accepted doctrine of European statesmen. Pitt was its stanchest advocate, and Burke its rational friend. Adam Smith, who assaulted it in 1776,[18] did not succeed in overthrowing it. Twenty-five years later, Henry Brougham controverted Smith's views.[19] It is not strange, therefore, that it found advocates among the colonists themselves. It was also far from being a one-sided question.