The verdict of history depends on who writes it, and the lessons of history depend on who reads it. Contemporary readers will look for the lessons of a 19th century international human rights initiative that involved treaties, international courts, and criminal prosecutions for crimes against humanity, all driven by the human-rights policy and the vast naval power of one pre-eminent state. Professor Jenny Martinez’ excellent book, The Slave Trade and the Origins of International Human Rights Law, presents the story of Great Britain’s partly successful effort to suppress the Atlantic slave trade while abiding by the limits imposed by international law as it then stood. This brief review will quickly recap some leading features of Professor Martinez’ story and then address one of the lessons she suggests can be drawn.
In the early 19th century the British government, responding to strong domestic pressure, undertook to suppress the transatlantic slave trade. Although the Royal Navy dominated ocean travel, Britain faced important legal obstacles. The slave trade was conducted on the high seas by vessels sailing under the protection of other sovereigns and was not itself unlawful. Principles of equal sovereignty, private property, and free navigation meant that seizing a slaver and releasing its human cargo was unlawful and could give rise to personal liability for British naval personnel.
Its great naval power constrained by law, the British government pursued its goal along two tracks. It entered into treaties with other maritime powers that participated in the trade. Those treaties imposed substantial limits on the trade, authorized naval vessels of the parties to enforce the agreements against one another’s merchant ships, and created so-called mixed commissions. The latter were maritime courts, staffed by judges from both parties, that adjudicated captures of alleged slavers. (Criminal jurisdiction was left to the parties’ domestic courts.) Britain entered into such treaties with Portugal, Spain, and the Netherlands in 1817, and with Brazil in 1826. Spain’s American colonies and Brazil were the main markets for slave imports; Martinez describes the combination of promises, threats, and appeals to shared interests that Britain brought to bear in obtaining Spanish, Portuguese and Brazilian legal endorsement of Royal Navy anti-slavery efforts, and a limited amount of active cooperation, from those treaty partners. (France and Britain entered into a treaty in 1831 that provided for mutual search but not mixed commissions.) As she documents, the enforcement program under the treaties had substantial success, though it did not fully eliminate the slave trade.
Absent from that list of treaty partners throughout the period when it mattered most was the United States. President Monroe submitted such a treaty to the Senate in 1824, but the Senate’s consent was given on conditions that Great Britain would not accept, and no treaty was ratified by the United States. Especially interesting to Americans today is that the proposed treaty had no mixed commissions, due to American constitutional scruples. In a mixed commission, foreign judges not appointed by the President of the United States would enforce American municipal law. Secretary of State John Quincy Adams took the position in negotiations with the British that the U.S. Constitution did not allow such an arrangement. His personal view may have been that it did: he and Attorney General William Wirt disagreed on this question in President Monroe’s cabinet deliberations, but Adams either changed his mind or, as an experienced diplomat, was prepared to put aside his private opinions. Only in 1862 was a suppression treaty, this time including mixed commissions, agreed to by the United States and Great Britain. Republican anti-slavery sentiment prevailed over remaining constitutional concerns. (The Senate’s debates on the 1862 treaty were conducted in closed executive session, so we have hardly any official records of views expressed on the constitutional issues.)
Treaties and mixed commissions were a powerful tool, at least when backed by the Royal Navy, but then as now, bilateral agreements did not change customary international law. Great Britain also sought to have the slave trade declared to be piracy by the general consent of nations. That principle, if adopted, would sweep aside all Britain’s difficulties: suspected pirate ships were subject to boarding and inspection, actual pirate ships could be seized and forfeited by any nation, and actual pirates were liable to be tried criminally and executed by any country that captured them. But even as more and more countries forbade the slave trade in their domestic law, entered into treaties for its suppression, and abolished slavery itself, 19th century customary international law did not come to regard the slave trade as piracy.
Over-all, the story was one of real but limited accomplishment. Acting in ways consistent with international law, Great Britain used its military, political, and economic power substantially to reduce the transatlantic slave trade. Martinez tells the story superbly, with detailed accounts of particular episodes, presentation of the available data about the slave trade and its suppression, and incisive discussions of international and United States domestic law. Martinez also does the important work of restoring this story to its important place in the history of international human-rights law and international criminal law.
The unavoidable but difficult question concerns the contemporary applicability of the history. Martinez suggests that international law augmented Britain’s raw power. Britain “used international law as one important tool for persuading other countries to abandon a widespread and profitable practice.” P. 14. After an initial attempt at unilateral action, “Britain found it could not rely on its military power alone but instead had to utilize that power in conjunction with cooperative legal action to achieve its goals.” Id. That cooperative legal action consisted of the treaties described above, but “at critical moments, Britain was forced to deploy its ‘hard’ powers, as well as its domestic law and courts, to bring reluctant treaty partners back into the legal fold. In short, neither raw coercive power nor international law alone was enough to achieve the abolition of the slave trade.” Pp. 14-15.
One might say instead, not that Britain used international law, but that British efforts to suppress the slave trade were constrained by international law, and that Britain’s decision to act lawfully limited those efforts. There was no legal bar on the slave trade to enforce, and British efforts to create one were unavailing. The slave trade treaties were somewhat effective, but Britain frequently had to pay for what it received, often in hard cash subsidies. Had the slave trade not been protected by international law, those treaties would have been unnecessary and the Royal Navy probably could have all but eliminated that traffic without the involvement of other nations. Maybe the basic international law principle of pacta sunt servanda made it possible for Britain, by binding its treaty partners, to achieve its goal more cheaply than through direct military action, but that is not clear. Under the treaties, governments had to be paid off and limits had to be accepted, and active cooperation seems to have been forthcoming only when the other parties wanted to give it anyway. One plausible interpretation is that through the treaties Great Britain did no more than buy the legal right to protect natural rights. Absent other aspects of international law, it could have done that for free.
It may well be that on balance the international rules that secured sovereignty, free navigation, and private property, were a good thing. Great Britain may have been wise not to cut down all those laws to get at the devil of the slave trade, and instead to work within their constraints. These are difficult questions, as is the question whether the rules of international law were, in a narrower sense, an aid or an obstacle to the accomplishment of this great object.
(John Harrison is a professor of law at the University of Virginia; he served as Deputy Assistant Attorney General, Office of Legal Counsel, United States Department of Justice, and Counselor on International Law to the Legal Adviser, United States Department of State.)