I don’t read many law reviews any more, but my eye fell on the current issue Yale Law Journal, which I cannot avoid as a former editor. This time, I was glad. There’s a fascinating article by Jenny Martinez, a Stanford law professor, “Antislavery Courts and the Dawn of International Human Rights Law.” http://yalelawjournal.org/117/4/martinez.html
The story begins with the banning of the slave trade by Britain and the United States in 1807 and 1808, respectively. Those bans, however, were just pieces of paper. Someone had to enforce them.
In a remarkable campaign in support of human rights, the Royal Navy aggressively policed the slave trade for the next sixty years, when the trade finally died out. Martinez concentrates on the years after the fall of Napoleon, when the British entered into bilateral treaties with several other European powers — France, Spain, and Portugal — to provide for the regular adjudication of slave ships seized by the Royal Navy. (The United States did not sign such a treaty with Britain until 1862.)

Schematic view of Atlantic slave ship, showing how slaves were stored for sleeping
The treaties established joint courts of the signatory nations that could rule on whether the seized ship was truly engaged in the slave trade. Each nation contributed one judge to the courts, which sat in Sierra Leone, Havana, and Rio de Janeiro. If the court found the ship was a slaver, its human cargo was set free and the ship was auctioned off. After a couple of decades, some of the courts approved seizures of empty slave ships, persuaded by the shackles and manacles on board that the ship should be forfeited by the owners.
Martinez estimates that these courts decided more than 600 cases and set free some 80,000 people from slave ships!
It’s a fascinating story (you can skim the law stuff). I recommend it.