 He wrote that Wilberforce and the Sierra Leone Company had "by means of their agents become slave traders themselves".He threatened to expose this situation, so he was sacked, with Wilberforce himself agreeing to the dismissal.In 1812, Thompson returned to his military duties, and, after serving in the south of France, was in 1815 attached as Arabic interpreter to an expedition against the Wahabees of the Persian Gulf, with whom he negotiated a treaty (dated January 1820) in which the slave trade was for the first time declared piracy.