The abolition of the slave trade was one of the great diplomatic themes over which the Great Powers both cooperated and clashed in the nineteenth century. For over two centuries, Britain had been the main European nation engaged in slave trading, its monopoly to bring Africans as slaves to the Spanish territories in the New World having been confirmed as late as the Peace of Utrecht in 1713. Between 1680 and 1780 over 2.1 million Africans were brought into slavery in the British Antilles alone. By the late eighteenth century, however, the abolition movement was well under way, especially in Britain. Its ideological background lay in part in humanitarian philosophy, as reflected in the liberal individualism of the French Revolution, in part in English Puritanism, especially the Quaker movement. The importation of slaves to its colonies was first prohibited by Denmark in 1792. Britain followed in 1807 and the U.S. Congress outlawed the slave trade one year later. The question was included at British Foreign Secretary Castlereagh's initiative on the agenda of the 1815 Vienna Conference. A declaration was passed in which the Great Powers proclaimed slave trade as "repugnant to the principles of humanity and of universal morality" and recognized "the obligation and necessity of abolishing it."
Nevertheless, while most European states enacted domestic legislation to prohibit and punish slave trade, no agreement was attained on concerted international action. Nor did Britain's efforts to agree on a universal system at London (1817–1818), Aix-la-Chapelle (1818), or Verona (1822) bear fruit. The declaration of principles was repeated without agreement on how to apply it in practice. Britain suggested the assimilation of slave trade with piracy with the attendant right of visit on foreign warships on vessels suspected of engaging in illegal trade. This was vigorously opposed by other powers, especially by France and the United States who saw the proposal as an illegitimate attempt to designate the British navy as the police of the seas.
In the absence of a general settlement, Britain concluded bilateral treaties providing for reciprocal rights of visit in strictly defined geographical locations and with regard to particular types of ships. Only military ships could carry out the visit, whose purpose was strictly confined to checking whether the suspected vessel was carrying slaves. A general convention associating slave trade with piracy was finally signed between Britain, France, Prussia, Austria, and Russia in 1841, again with both limitations as to location and manner of carrying out the visits. However, France refused to ratify the convention and concluded a bilateral treaty in 1845 that provided, instead of a right of visit, the right to verify the flag of suspected ships, with the assumption that any enforcement would be taken by the flag state. Also the United States remained initially outside the general convention that it saw as serving predominantly British interests. The need to take more efficient measures, however, induced the United States to sign a treaty on reciprocal visits with Britain in 1861.
The virtual cessation of slave trade on Africa's western coast prompted Britain to conclude treaties also with Egypt, Turkey, and Italy in the 1870s and 1880s in order to implement the prohibition of trading in the Indian Ocean. A provision (Article IX) was also included in the Berlin Act of 1885 in which the Great Powers declared that their territories in the Congo basin would not be used "as market or means of transit for the trade in slaves."
At the initiative of the Pope and of Lord Salisbury, King Leopold II of the Belgians invited the signatories of the Berlin Act, as well as Luxembourg, Persia, and Zanzibar, to a conference in Brussels to take further measures against slavery and slave trade not only at sea—after all, slaving dhows could easily escape formal navies—but at the source in Africa. Despite the shared humanitarian hyperbole, the Brussels Conference dragged on from November 1889 until a deal was struck early the following summer that authorized King Leopold to deviate from the free trade provisions of the 1885 Berlin Act ostensibly to finance the antislavery measures in his Independent State of the Congo.
The General Act of the Brussels Conference Relative to the African Slave Trade was adopted on 2 July 1890. It provided for far-reaching economic, military, and legal measures, in over one hundred articles, to combat slave trade. Measures to be taken in Africa included the strengthening of the local administrations, establishment of observation posts, construction of roads and railways, and communication mechanisms to substitute for the practice of human porters that had contributed to slavery. Such "good government" measures also included increased security on the roads and the prohibition of the importation of firearms and munitions into territories where slave trading was practiced. An international office was set up in Zanzibar to give instructions and assistance on the repression of the slave trade in countries of destination; national laws and regulations were to be communicated to the office which would then circulate that information to other powers.
On the right of visit, the conference agreed on a compromise that restricted this right to the verification of the flag of the suspected vessel. Detailed instructions were provided concerning the ship's papers and the use of the flag. Only vessels with a tonnage below five hundred tons could be inspected (most slave trading in the Indian Ocean took place by small vessels to enable unmarked landings). Enforcement jurisdiction would as the main rule remain with the flag state. However, the capturing vessel was authorized to bring suspected ships to the closest harbor and follow through the enquiry conducted by the flag state's national officials. A vessel condemned of illegal traffic would become the property of the captor. Liberated slaves were to be accorded protection by national authorities.
Most states ratified the act within one year. As the French National Assembly continued to object, the government nevertheless remained bound by its earlier bilateral agreements.
The Brussels Act was abrogated by the Peace of Saint-Germain-en-Laye in 1919. In the twenty-first century, the prohibition of slavery and the slave trade are contained in the 1926 Slavery Convention and the Supplementary Convention of 1956. Analogous practices such as traffic in persons, prostitution, and debt bondage—more important in the early twenty-first century than chattel-like slavery—are the object of increasing regulation by the United Nations and international organizations.
Fischer, G. "Esclavage et le droit international." Revue générale de droit international public 61 (1957): 71–101.
Fisher, H. "The Suppression of the Slave Trade." International Law Quarterly 1 (1950): 28–51, 503–522.
Kern, Holger Lutz. "Strategies of Legal Change: Great Britain, International Law and the Abolition of the Transatlantic Slave Trade." Journal of the History of International Law 6 (2004): 233–258.
Thomas, Hugh. The Slave Trade. The Story of the Atlantic Slave Trade, 1440–1870. New York, 1997.