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Their second African journey from 1870-3 was to report on the slave trade along the Nile . The internal slave trade within the United States is unaffected by the law , and illegal slaves continue to be smuggled into the country . ” That program took twenty years , until Parliament abolished the slave trade throughout the Empire in 1807 . Although the law of March 22 , 1794 , prohibiting the slave trade between the United States and foreign countries , did not specifically direct the revenue cutters to aid in its enforcement , " they were nevertheless instructed to do so ; and their connection with efforts to suppress the traffic , begun under this Act , did not cease until the occasion for such efforts had entirely disappeared . While its ships supported commerce and diplomacy in the far flung corners of the world and suppressed piracy in the Caribbean and the slave trade off the African coast , as before , the navy was limited to support of the merchant class , and it was still not assigned any broad national roles during peacetime .