This marks the beginning of a long series of treaties between England and other powers looking toward the prohibition of the traffic by international agreement.  During the years 1810-1814 she signed treaties relating to the subject with Portugal, Denmark, and Sweden.[13] May 30, 1814, an additional article to the Treaty of Paris, between France and Great Britain, engaged these powers to endeavor to induce the approaching Congress at Vienna “to decree the abolition of the Slave Trade, so that the said Trade shall cease universally, as it shall cease definitively, under any circumstances, on the part of the French Government, in the course of 5 years; and that during the said period no Slave Merchant shall import or sell Slaves, except in the Colonies of the State of which he is a Subject."[14] In addition to this, the next day a circular letter was despatched by Castlereagh to Austria, Russia, and Prussia, expressing the hope “that the Powers of Europe, when restoring Peace to Europe, with one common interest, will crown this great work by interposing their benign offices in favour of those Regions of the Globe, which yet continue to be desolated by this unnatural and inhuman traffic."[15] Meantime additional treaties were secured:  in 1814 by royal decree Netherlands agreed to abolish the trade;[16] Spain was induced by her necessities to restrain her trade to her own colonies, and to endeavor to prevent the fraudulent use of her flag by foreigners;[17] and in 1815 Portugal agreed to abolish the slave-trade north of the equator.[18]

68. Action of the Powers from 1814 to 1820. At the Congress of Vienna, which assembled late in 1814, Castlereagh was indefatigable in his endeavors to secure the abolition of the trade.  France and Spain, however, refused to yield farther than they had already done, and the other powers hesitated to go to the lengths he recommended.  Nevertheless, he secured the institution of annual conferences on the matter, and a declaration by the Congress strongly condemning the trade and declaring that “the public voice in all civilized countries was raised to demand its suppression as soon as possible,” and that, while the definitive period of termination would be left to subsequent negotiation, the sovereigns would not consider their work done until the trade was entirely suppressed.[19]

In the Treaty of Ghent, between Great Britain and the United States, ratified February 17, 1815, Article 10, proposed by Great Britain, declared that, “Whereas the traffic in slaves is irreconcilable with the principles of humanity and justice,” the two countries agreed to use their best endeavors in abolishing the trade.[20] The final overthrow of Napoleon was marked by a second declaration of the powers, who, “desiring to give effect to the measures on which they deliberated at the Congress of Vienna, relative to the complete and universal abolition of the Slave Trade, and having, each in their respective Dominions, prohibited without