restriction their Colonies and Subjects from taking any part whatever in this Traffic, engage to renew conjointly their efforts, with the view of securing final success to those principles which they proclaimed in the Declaration of the 4th February, 1815, and of concerting, without loss of time, through their Ministers at the Courts of London and of Paris, the most effectual measures for the entire and definitive abolition of a Commerce so odious, and so strongly condemned by the laws of religion and of nature."[21]

Treaties further restricting the trade continued to be made by Great Britain:  Spain abolished the trade north of the equator in 1817,[22] and promised entire abolition in 1820; Spain, Portugal, and Holland also granted a mutual limited Right of Search to England, and joined in establishing mixed courts.[23] The effort, however, to secure a general declaration of the powers urging, if not compelling, the abolition of the trade in 1820, as well as the attempt to secure a qualified international Right of Visit, failed, although both propositions were strongly urged by England at the Conference of 1818.[24]

69. The Struggle for an International Right of Search, 1820-1840. Whatever England’s motives were, it is certain that only a limited international Right of Visit on the high seas could suppress or greatly limit the slave-trade.  Her diplomacy was therefore henceforth directed to this end.  On the other hand, the maritime supremacy of England, so successfully asserted during the Napoleonic wars, would, in case a Right of Search were granted, virtually make England the policeman of the seas; and if nations like the United States had already, under present conditions, had just cause to complain of violations by England of their rights on the seas, might not any extension of rights by international agreement be dangerous?  It was such considerations that for many years brought the powers to a dead-lock in their efforts to suppress the slave-trade.

At first it looked as if England might attempt, by judicial decisions in her own courts, to seize even foreign slavers.[25] After the war, however, her courts disavowed such action,[26] and the right was sought for by treaty stipulation.  Castlereagh took early opportunity to approach the United States on the matter, suggesting to Minister Rush, June 20, 1818, a mutual but strictly limited Right of Search.[27] Rush was ordered to give him assurances of the solicitude of the United States to suppress the traffic, but to state that the concessions asked for appeared of a character not adaptable to our institutions.  Negotiations were then transferred to Washington; and the new British minister, Mr. Stratford Canning, approached Adams with full instructions in December, 1820.[28]