The Cherwell Convention was a multilateral accord, the most stringent of the League's anti-slavery treaties. It was originally drafted by Beowulf in response to Mesa's development in the field of genetic slavery, and signed in 1651 PD.
All signatories endorsed the equation of slavery with piracy, and agreed that the naval forces of any signatory had the right to stop, search and confiscate merchant vessels transporting slaves while sailing under the protection of their flags, and, more importantly, that they had the right to try the crews of those confiscated vessels for piracy, which was punishable by death in many star nations. The "Equipment Clause" addition to the Convention was not agreed to by all those agreeing to the Convention. Not all star nations had signed the additional clause, and not all required their armed forces to strictly enforce the Convention with or without the Clause, however.
The Cherwell Convention was the one interstellar accord to which both the Star Kingdom of Manticore and the Republic of Haven were signatories and which remained in effect throughout all the tension and open hostilities between them. Both had excellent records of enforcement.
The Silesian Confederacy signed the Convention, though only under threat of Manticoran military action during the reign of Queen Adrienne. It, and its component star systems, were very spotty enforcers of the agreement. (CS1, SI2)
Equipment clause Edit
The standard response of slaver-traders about to be overhauled was to jettison the slaves they carried into space and then try to use their absence as a proof of innocence. In order to put an end to that practice, an amendment was added to the Cherwell Convention: the "equipment clause", as proposed by Roger II of Manticore. It held that any ship equipped as a slaver was in fact a slaver, whether it had slaves on board or not.
Not all signatories of the Convention supported this clause (most notably Solarians and Silesians), but Manticoran and Havenite navies enforced it strictly since its very inception. In fact, the two star nations adopted the official position that a slaver crew found without a living cargo would be immediately tried for mass murder and, if convicted, executed by spacing. (CS1)
Almost all major star nations were signatories, though that did not prevent many from ignoring the provisions of the Convention when it suited them. Historically, the star nations which most reliably enforced the Convention in their regions were the Star Kingdom of Manticore and the Republic of Haven. On the other hand, the Silesian Confederacy and Solarian League often suffered from deep corruption regarding the issue, despite the fact that they were official signatories. Only a few Naval officers from these polities (mostly Solarians) had a good record of enforcement. (CS1)