The Navigation Act of 1651 mandated that only English vessels, or vessels of the nation that produced the goods, would be allowed to import goods into the English Commonwealth territories. Essentially, it banned foreign or third-party nations' ships from exporting goods to England or English colonies and was mostly targeted at the Dutch.
The first Navigation Act was aimed at the Dutch because of a failed alliance between the English and the United Provinces of the Netherlands. It aimed to impair the Dutch trade economy. Instead of free trade with England, the Dutch could only legally export cheese and butter from Holland to English territory. Eventually, conflicts and tension would lead to the First Anglo-Dutch War in 1652.