Key figures: Lord Frederick North, King George III, John Adams, Admiral Richard Howe
Summary
The American Prohibitory Act (formally An Act to prohibit all trade and intercourse with the American colonies, 16 Geo. 3 c. 5) received royal assent on December 22, 1775, and took operational effect through 1776. The legislation was the most sweeping commercial measure Parliament had directed against the colonies: it withdrew the Crown’s protection from colonial trade, declared all American ships and their cargoes forfeit to the Crown as lawful prize, and authorized the Royal Navy to seize and condemn any vessel found trading with the thirteen colonies. The act effectively placed the colonies outside the British economic and legal system. Colonial leaders, including John Adams, interpreted it as a de facto declaration of independence by the Crown itself — Parliament had, in Adams’s reading, expelled the colonies from the empire before the colonies formally chose to leave. The Prohibitory Act accelerated both the Continental Congress’s push to open American ports to foreign trade and the broader movement toward declaring independence in the summer of 1776.
Background: From Restraining Acts to Total Embargo
The Prohibitory Act was the culmination of a series of escalating economic measures. The New England Restraining Act of March 1775 had already prohibited the New England colonies from trading with any nation outside Great Britain and its colonies, and from fishing the North Atlantic banks — a severe blow to the maritime economies of Massachusetts, Rhode Island, Connecticut, and New Hampshire. A second Restraining Act in April 1775 extended these restrictions to Pennsylvania, New Jersey, Maryland, Virginia, and South Carolina. These measures fell short of a total blockade, however, and were widely evaded. Lord North’s ministry concluded that only a comprehensive act covering all thirteen colonies and authorizing naval seizure would bring the rebellion to heel economically.
The bill was introduced in Parliament in October 1775 and passed both houses, receiving royal assent on December 22, 1775. Its operative date for seizure authority was March 1, 1776, giving colonial merchants a brief window, though the Royal Navy began intercepting colonial shipping well before that date.
Terms and Provisions
The act’s central provisions were far-reaching:
- Trade prohibition: All trade and commerce with the thirteen colonies was declared unlawful. No British subject could legally send goods to or receive goods from the colonies.
- Forfeiture of ships and cargoes: Any vessel caught trading with the colonies was declared forfeit to the Crown “as if the same were the ships and effects of open enemies” — the language deliberately assimilating American colonists to foreign adversaries rather than subjects in rebellion.
- Naval seizure authority: Royal Navy captains were empowered to stop, board, and condemn any vessel found in colonial waters or engaged in colonial trade, with the proceeds of condemned vessels to be divided among the naval crews as prize money.
- Impressment: The crews of seized American vessels could be compelled into service in the Royal Navy — a provision that transformed the act from an economic measure into one with direct military implications for thousands of colonial mariners.
- Withdrawal of royal protection: By treating colonial ships as enemy property, the act implicitly withdrew the Crown’s protection from colonial subjects engaged in commerce, a legal step of profound constitutional significance.
Colonial Reactions: Adams and the “Act of Independency”
The colonial response to the Prohibitory Act was swift and politically galvanizing. John Adams, then a Massachusetts delegate to the Continental Congress, described it in a March 23, 1776 letter to General Horatio Gates as “the Act of Parliament called the restraining Act, or prohibitory Act, or piratical Act, or plundering Act, or Act of Independency, for by all these Titles is it called.” Adams added: “I think the most apposite is the Act of Independency, for King Lords and Commons have united in Sundering this Country and that I think forever.” In other correspondence Adams wrote that the act “throws thirteen colonies out of the royal protection, levels all distinctions, and makes us independent in spite of our supplications and entreaties.”
The political logic was stark: if the Crown had already withdrawn its protection and declared colonial commerce unlawful, the colonists could no longer claim to be loyal subjects seeking redress — they were, in the eyes of British law, already enemies. This reading removed a significant argument against independence: the claim that severing ties with Britain would be an act of aggression. Adams and other independence advocates used the Prohibitory Act as evidence that Britain had already acted aggressively, and that independence was now a matter of legal recognition rather than political rupture.
Congress’s Response: Opening American Ports
The Continental Congress responded to the Prohibitory Act on two tracks. On March 23, 1776, it passed a Privateering Resolution authorizing American shipowners to arm their vessels and seize British ships as lawful prize — a direct economic counter to the Royal Navy’s seizure authority under the Prohibitory Act. This formalized American privateering, which rapidly became a significant commercial enterprise: over the course of the war, American privateers captured an estimated 600 British vessels.
More consequentially, on April 6, 1776, Congress voted to open American ports to commerce with all nations except Great Britain. This measure, drafted with input from John Adams and Charles Lee, effectively nullified the Navigation Acts — the body of mercantilist law that had governed colonial trade since the 1650s and required colonial exports to flow through British ports. By welcoming French, Dutch, Spanish, and Danish vessels, Congress both defied the Prohibitory Act’s embargo and laid the diplomatic groundwork for the foreign alliances that would prove decisive in the war.
The Royal Navy Blockade and Economic Impact in 1776
Admiral Richard Howe, appointed to overall naval command in North America in 1776, inherited an enormous operational challenge: the American coastline extended over three thousand miles, the Royal Navy’s available force was initially inadequate to seal it, and colonial ports were numerous and shallow enough to frustrate deep-draft warships. Nevertheless, the navy sustained a partial blockade that had measurable economic effects throughout 1776. British warships interdicted merchant traffic along the New England coast, harassed Chesapeake Bay commerce, and blockaded major harbors including Boston (before the March evacuation), Newport, New York (after its capture in September), and later Philadelphia.
The blockade disrupted the colonial export trade in tobacco, timber, fish, and naval stores — commodities for which the colonies depended on European markets. Colonial imports of manufactured goods, gunpowder, and military supplies were severely constrained, a problem Congress attempted to address through the covert French and Spanish supply networks established in 1776. The economic dislocation caused by the blockade contributed to the inflationary pressures already driving depreciation of Continental currency: with fewer goods flowing through the economy, prices rose and confidence in paper money fell.
Despite these pressures, the blockade never achieved the stranglehold the North ministry had anticipated. The length of the coastline, the shallowness of many colonial inlets and rivers, the activity of American privateers, and the eventual entry of France into the war (1778) collectively prevented Britain from achieving the complete commercial isolation the Prohibitory Act had envisioned.
Significance
The Prohibitory Act occupies a pivotal place in the economic and political history of 1776. Economically, it transformed the colonies’ commercial relationship with the Atlantic world: by outlawing the existing trade structure, it forced colonists toward the open-port system, toward privateering, and toward the foreign alliances that reshaped trans-Atlantic commerce for decades. Politically, its framing — treating colonists as “open enemies” — handed independence advocates a rhetorical and legal argument they exploited effectively. One of the twenty-seven grievances cited in the Declaration of Independence refers to Parliament having “cut off our Trade with all parts of the world.” The Prohibitory Act was thus not merely an episode in economic history; it was one of the legislative acts that made American independence, in Adams’s phrase, a fact before it was formally proclaimed.