What did the navigation acts require in relation to colonial imports?

Here's a description of what the Navigation Act was, and in this it also answers your question!

The Navigation Acts were a series of English laws that restricted colonial trade to the mother country. They were first enacted in 1651 and throughout that time until 1663,[1] and were repealed in 1849. They reflected the policy of mercantilism, which sought to keep all the benefits of trade inside the Empire, and to minimise the loss of gold and silver to foreigners. They prohibited the colonies from trading directly with the Netherlands, Spain, France, and their colonies. The original ordinance of 1651 was renewed at the Restoration by Acts of 1660, 1663, 1670, and 1673, with subsequent minor amendments. The Acts formed the basis for English overseas trade for nearly 200 years. Additionally the Acts restricted the employment of non-English sailors to a quarter of the crew on returning East India Company ships.

The major impetuses for the Navigation Acts were the ruinous deterioration of English trade in the aftermath of the Eighty Years' War, and the concomitant lifting of the Spanish embargoes on trade between the Spanish Empire and the Dutch Republic. The end of the embargoes in 1647 unleashed the full power of the Amsterdam Entrepôt and other Dutch competitive advantages in world trade. Within a few years, English merchants had practically been overwhelmed in the trade in the Iberian Peninsula, the Mediterranean and the Levant. Even the trade with English colonies (partly still in the hands of the royalists, as the English Civil War was in its final stages and the Commonwealth of England had not yet imposed its authority throughout the English colonies) was "engrossed" by Dutch merchants. English direct trade was crowded out by a sudden influx of commodities from the Levant, Mediterranean and the Spanish and Portuguese empires, and the West Indies via the Dutch Entrepôt, carried in Dutch ships and for Dutch account.[2]

The obvious solution seemed to be to seal off the English and Scottish markets to these unwanted imports. A precedent was the Act the Greenland Company had obtained from Parliament in 1645 prohibiting the import of whale products into England, except in ships owned by that company. This principle was now generalised. In 1648 the Levant Company petitioned Parliament for the prohibition of imports of Turkish goods "...from Holland and other places but directly from the places of their growth."[3] Baltic traders added their voices to this chorus. In 1650 the Standing Council for Trade and the Council of State of the Commonwealth prepared a general policy designed to impede the flow of Mediterranean and colonial commodities via Holland and Zeeland into England.[4]

On the whole, the Acts of Trade and Navigation were obeyed, except for the Molasses Act of 1733, which led to extensive smuggling because no effective means of enforcement was provided until the 1750s. Stricter enforcement under the Sugar Act of 1764 became one source of resentment of Great Britain by merchants in the American colonies. This in turn helped push the colonies to start the American Revolution in the late 18th century, even though the consensus view among modern economic historians and economists is that the "costs imposed on [American] colonists by the trade restrictions of the Navigation Acts were small.

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