Privateering became less effective over the course of the 19th century, and remarkably unpopular on the world stage following the Crimean War and the Treaty of Paris of 1856. At this point, privateering in big empires such as Britain and Spain had been on the decline for a good while. In general, that can be attributed to a couple factors:

(1) the increasing profitability of overseas trade increased the opportunity cost of privateering and made it an untenable option for most merchants, and

(2) the increasing wealth of the English Crown facilitated the growing professionalization of the British navy, drastically outpacing the fighting capacity of privately outfitted privateer vessels.^(1)

As part of the Treaty of Paris of 1856, the signatories introduced new rules of naval warfare including the complete abolition of privateering. In April, the signatories extended the agreement to become a general declaration respecting maritime law. In total, 55 states ratified the declaration, but the United States was not among them. William L. Marcy, the Secretary of State under then-president Franklin Pierce, refused to sign for a few reasons. He argued that the first proposition of the declaration (which audaciously declared that “privateering is, and remains, abolished”) was false in practice. Privateering did, after all, still exist - the US still took part in it. Furthermore, Marcy regarded "the proposition as directed at the maritime powers of secondary rank; as tending to give the sovereignty of the seas exclusively to those States who possess vast naval establishments.” Marcy reasoned that privateering was a democratic way for a nation to strengthen its naval power through private volunteers.^(2)

Nevertheless, in the US at this time, support for privateering was still an unpopular position. There were some naval strategists who pushed for it to become the express US naval strategy during the Civil War to further enforce trade blockades, but it never caught on because it was too diplomatically incendiary and it was nearly as unprofitable for US merchants as British ones. Naval ships got heavier, more expensive, and better-armed. Merchant ships, in contrast, made more and more money through trade and had a lower potential to combat enemy naval ships over time. Privateering naturally declined as a result.

^(1) Hillmann and Gathmann, “Overseas Trade and the Decline of Privateering,” 3.

^(2) William L. Marcy, “Privateering-Secretary Marcy’s Manifesto.”