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Vienna and the Abolition of the Slave Trade

By: Randall Lesaffer

In April 1822, sailors from the British warships HMS Iphigenia and HMS Myrmidon, after a brief but fierce fight, captured two Spanish and three French slave ships off the coast of what is now Nigeria. Prize crews sailed the ships to Freetown in Sierra Leone, where the international mixed commission which was competent to hear cases regarding the slave trade decided to liberate the slaves found on the Spanish schooners, as well as those slaves found on a Portuguese ship which the British naval vessels had taken earlier.

With this story, the American international lawyer Jenny Martinez opens her book on the abolition of the slave trade in the 19th century. The actions of the British navy to fight the international, and particularly the Atlantic, slave trade, the establishment of mixed commissions, and the ensuing liberation of almost 80,000 slaves by those international tribunals were pursuant to a growing web of treaties which prohibited the international slave trade, and eventually slavery itself. In this development, the Vienna Congress of 1814–1815 played a seminal role.

In the historiography of international law, the Congress of Vienna not only holds pride of place for having achieved a new political and legal order of Europe that would last for over half a century, but Vienna is also much quoted for having given birth to the first multilateral codifications of international law.

Since the 19th century, international legal scholars have distinguished between two categories of treaties, traités-lois and traités-contrats. While the latter category, traités-contrats or contract treaties apply existing international law to create concrete rights and obligations between the parties, the former category of traités-lois or law-making treaties codify existing rules of international customary law, change them or introduce new international law. Almost by necessity, the latter type of treaties are multilateral.

The treaties made at the Congress of Vienna contained regulations regarding three subjects of international law: the ranking and order of precedence of diplomatic agents (Regulation on the Precedence of Diplomatic Agents of 19 March 1815, 64 CTS 1), navigation on international rivers (Regulation for the Free Navigation of Rivers of 24 March 1815, 64 CTS 13-1), and the abolition of the slave trade. Whereas the Declaration of the Eight Courts Relative to the Universal Abolition of the Slave Trade of 8 February 1815 (63 CTS 473) was the least concrete in terms of the legal impositions it made, it was of great historic significance.

The Declaration was signed by the seven leading powers of the anti-Napoleonic coalition – Austria, Britain, Prussia, Russia, Portugal, Spain, and Sweden – as well as France. It was incorporated into the Final Act of the Vienna Congress of 9 June 1815 (64 CTS 453) as Annex XV. The Declaration was an achievement of British diplomacy, and of its major representative at Vienna, Robert Stewart, Lord Castlereagh (1769–1822).

If, during the early 19th century, Britain had become the champion among European States for the abolition of the slave trade, this was largely the merit of a movement which sprang from civil society. During the final decades of the 18th century, Britain, as well as the American colonies which were soon to become the United States, saw the emergence of a strong and vocal movement that strove for the abolition of slavery. This movement, which was also driven by economic motives and inspired by sensitivities about human dignity flowing from the Enlightenment, had its strongest roots in radical, puritan Protestant circles. After having scored a major success before the courts in Somerset v. Stewart in 1772 (98 English Reports 499), wherein the holding of slaves on English soil was banned, the abolition movement turned its guns against the international slave trade. After Parliament had rejected several proposals to enact legislation to that extent, the fortunes of the movement changed when it allied its cause to the war effort against France and targeted the French slave trade. In 1806, Parliament passed the Foreign Slave Trade Act (46 Geo. 3, c. 52 (Eng.)), which forbade British subjects to trade in slaves with France or its allies. A year later, the Act for the Abolition of the Slave Trade (47 Geo. 3, c. 36 (Eng.)) expanded the prohibition to the slave trade as a whole. In 1808, the United States followed suit.

During the Napoleonic wars and the War of 1812 against the US, the British navy used its rights under the laws of war and neutrality to act against enemy and neutral vessels to stop the slave trade. As this occurred in contravention to established neutrality law and carried dangers for the relations with different neutral countries, British diplomacy endeavoured to conclude bilateral treaties with other powers whereby these powers accepted partial restrictions against trade in certain geographical areas, as in the treaties with Portugal of Rio de Janeiro of 19 February 1810 (61 CTS 41-1) and of Vienna of 21 January 1815 (63 CTS 453).

The prospect of peace, however, forced the peace movement to change tack. The First Paris Peace Treaty of 30 May 1814 (63 CTS 171) between the allies and France made this painfully clear. In one of the separate articles, concluded between Britain and France, it was stipulated that France would join Britain in its endeavour to attain a universal prohibition of the slave trade. The same article, however, made allowances for the French to wait for the enactment of national legislation to quell the slave trade for five more years, which in practical terms meant a step back from what Britain had been doing against the French slave trade during the war. This clause triggered a massive campaign within Britain which helped to force the hand of British diplomacy to push the issue at Vienna.

The British followed a dual strategy. On the one hand, they tried to move towards a general, multilateral convention against the slave trade. This proved to be particularly difficult because of French resistance. On the other hand, success was attained by including prohibitions of the slave trade in bilateral treaties with other countries, including – apart from Portugal – the Netherlands (Treaty of London of 13 August 1814, Art. 8 – 63 CTS 321) and the US (Treaty of Ghent of 24 December 1814, Art. 10 – 63 CTS 421).

In the face of French resistance, which was seconded by Spain and Portugal, the British failed to attain an immediate, general prohibition of the slave trade in a multilateral treaty. The establishment of an international commission also proved unattainable. But on 8 February 1815 the eight leading powers did sign a Declaration which condemned the slave trade as ‘repugnant to the principles of humanity and universal morality’, making direct reference to public outcry against it in ‘all civilised nations’. Regardless of this strong language, the Declaration remained more at the level of expressing a lofty cause than imposing concrete obligations, except for the commitment to start negotiations about general abolition and its timing.

Although the abolition movement felt a lot of disappointment over this result, in the most ironic of ways it served to clear a major obstacle towards general abolition. After Napoleon reassumed power upon his escape from Elba in March 1815, he moved to abolish the slave trade in order to placate the Vienna Congress. After Waterloo, the ban was sustained by the restored Bourbon regime. Whereas no general treaty of abolition of the slave trade materialised after Vienna, over the next decades many States moved to enact abolition through national legislation. As a more direct result of the Vienna regulation, in 1817 Britain succeeded in concluding several bilateral treaties, among others with Portugal (28 July 1817, 67 CTS 373) and Spain (23 September 1817, 68 CTS 45) by which mixed commissions were set up to deal with slave trade issues. It was under these latter two treaties that the Freetown mixed commission operated in the above-mentioned case of 1822. On 20 December 1841, the five great powers of Europe concluded a treaty whereby they committed themselves to promote the abolition of slave trade and recognised a right to stop and search each other’s merchant vessels in certain waters in order to enforce it (92 CTS 437).

The Vienna Declaration has been rightly credited with having introduced abolition of the slave trade as a principle in general international law. As such, it became an inspiration and point of reference for the fight for general abolition. But it was not without its dark side. The connection made to the ‘civilising mission’ in the text of the Vienna Declaration would also play its role as abolition grew into a major justification for the ‘Scramble for Africa’, the speedy colonisation of Sub-Saharan Africa by European powers between the 1870s and the 1910s. The General Act of the Berlin Conference of 26 February 1885 bears testimony to this (165 CTS 485). In its Article 9, it stated that abolition was a principle of the law of nations. But, more to the point, the text also granted the powers the right to ‘employ all means and their power’ to quell the slave trade in the Congo area. It was the same Berlin Conference which granted Congo as a Free State to the Belgian King Leopold II (1865–1909), whose brutal regime would lead to one of the largest genocides in human history. Five years later, the General Act of the Brussels Anti-Slavery Conference of 2 July 1890 went as far as to call ‘the progressive organisation of administrative, judicial, religious, and military service in the African territories’ to be ‘the most effective means of counteracting the slave-trade’ (Article 1.1, 173 CTS 293), thus expressly making colonisation into an instrument of abolition.


Jean Allain (ed.), The Legal Understanding of Slavery: From the Historical to the Contemporary(Oxford: Oxford University Press, 2012).

David Brion Davis, The Problem of Slavery in the Age of Revolution 1770–1823 (Oxford: Oxford University Press, 1999).

Bernard Edwards, Royal Navy Versus the Slave Traders: Enforcing Abolition at Sea 1808–1898 (Barnsley: Pen & Sword Maritime, 2007).

Adam Hochschild, King Leopold’s Ghost. A Story of Greed, Terror, and Heroism in Colonial Africa (Boston: Houghton Mifflin, 1998).

Adam Hochschild, Bury the Chains: Prophets and Rebels in the Fight to Free an Empire’s Slaves (Boston: Houghton Mifflin, 2005).

Jenny S. Martinez, The Slave Trade and the Origins of International Human Rights Law (Oxford: Oxford University Press, 2012).

Hugh Thomas, The Slave Trade: The Story of the Atlantic Slave Trade, 1440–1870 (New York: Simon & Schuster, 1997).

David Van Reybrouck, Congo: The Epic History of a People (London: Ecco, 2014).