'Navigation Acts' were all about protecting English ( and Colonial) shipping from foreign competition and securing the profits of overseas trade for English (and colonial) merchants. The earliest of these Acts can be traced as far back as 1381 but the Act of 1651 is, at first glance, surprising. England was now a Republic, since the execution of King Charles I in January 1649, and was Protestant. The States General, better known as Holland, was the country whose trade would be hardest hit by the Navigation Act and it was also a Protestant Republic. England and Holland should have been natural allies in the mid seventeenth century struggle between Royalists and Republicans and between Protestantism and Roman Catholicism, but they ended up at War (First Anglo-Dutch War 1652-54) and the 1651 Navigation Act was a major factor in this. So what went wrong?
Both England and the Dutch States General had powerful merchant fleets and an interest in colonial expansion in the early seventeenth century, but from 1621 the Dutch were involved in the 30 Years War with Spain. Spain was extremely rich with a vast Empire in the Americas and during this war its markets were closed to the Dutch, but they were open to the English. In 1648 though this war ended and the Dutch were once again able to compete with English merchant ships in Spanish markets. English merchants had already been driven from the lucrative spice trade in the Dutch East Indies and now were also facing increased competition in the Mediterranean and the West Indies from the Dutch.
Despite all this, the English Parliament had decided to seek alliance with the Dutch and in 1650 had sent Oliver St John and Walter Strickland to try to negotiate this. In the same year a Commonwealth Ordinance had banned foreign ships from trading in English colonies. By 1651 negotiations with the Dutch had broken down and St John and Strickland returned to England. With no prospect of alliance with the Dutch, in August the English Council of State proposed a Navigation Act against Dutch trade competition and this was passed by Parliament in October 1651.
The 1651 Navigation Act forbade the importation of goods into England except in English vessels or vessels of the country of the origin of the goods. Although it applied to all nations it was clearly aimed at the Dutch who were by far the pre-eminent competitors to English merchant ships. It was intended to hamper Dutch trade and it would limit Dutch trade with England and her colonies to little more than butter and cheese. It would be a hammer blow to the sizable Dutch fishing industry, which depended heavily on the export of fish oil and salted fish to England. Conversely, it would be a boost to the English merchant fleet.
By 1652, England and the Dutch States General were at war, the First Anglo-Dutch War, which ended in 1654. Ultimately, by the end of the seventeenth century, England had broken Dutch maritime power and had emerged as the world's leading sea power, a position she held until the twentieth century.