The two Anglo-Spanish treaties to abolish the Cuban slave trade established a structure of courts and officials in Cuba and on the African west coast to pronounce sentence on every slave ship captured under the treaties' provisions. The treaties also contained clauses guaranteeing the freedom of Africans found on captured slavers. The courts of mixed commission, located in Sierra Leone and Havana, were to free all Africans from condemned slave ships and guarantee their liberty through the issuance of certificates of emancipation. According to the 1817 treaty, all Africans liberated as a result of decisions in the Sierra Leone court would remain in that colony under British supervision and all Africans freed at Havana were to be the responsibility of the Spanish colonial authorities. In Sierra Leone the British colonial officials accepted their role as guardians of the liberty of these freed Africans, although demands for African labourers in the West Indies after 1833 caused considerable exploitation. On the other side of the ocean the fate of the emancipados, as the liberated Africans came to be known, became in Cuba as it did in Brazil a form of slavery in many respects worse than that of legal slavery. Because the emancipado class was brought into existence by treaty, their treatment emerged as one of the thorniest issues at stake between the British and Spanish governments, with angry diplomatic exchanges continuing until long after the Cuban slave trade itself finally had ended.

Swirls of historical controversy still surround both Turnbull's role in a mass slave conspiracy in 1844 and the very existence of the conspiracy itself. Duvon C. Corbitt, writing in the 1930s, said: ‘There are few incidents in the history of Cuba about which there is more uncertainty than there is about the slave uprising of 1843, and the slave conspiracy supposed to have been discovered the following year.’ Historians continue to take diametrically opposed positions in their interpretation of what happened. Franklin Knight has claimed that ‘the supposed slave “revolt” of 1844 had absolutely no foundation in fact’, while Arthur F. Corwin not only accepts the fact of a slave conspiracy but, following an earlier generation of Cuban historians, sees Turnbull as the cause of the revolt and the one who conceived the idea. Another American historian, Gwendolyn Midlo Hall, has concluded, ‘there is little doubt that the conspiracy among the estate slaves was very real and extraordinarily well organized’.

Peninsular historians, anxious to demonstrate the reality of a British abolitionist offensive against Spain's major colony, wrote some of the earliest accounts of the events of the 1844 uprisings. Two semi-official Spanish histories which appeared in the 1870s magnified British abolitionist influence within Britain itself and overseas. British abolitionists dominated successive British governments and their sole purpose was to destroy slavery, regardless of the means used. After succeeding in abolishing slavery within the British empire, they sought to extend their social revolution to other slave states.

Spain's colonial empire saw the beginning and the end of the transatlantic slave trade. In one of the ironies of history, the abolition of the commerce in African slaves preceded the loss of Spain's last American possessions, reversing the process begun nearly four hundred years before when Spain's conquest of the Indies led to the beginning of the Atlantic slave trade. Even before the majority of Spain's American colonies received their political independence in the period 1810–25, the question of the African slave trade in Spain's overseas dominions involved mainly the plantation colonies, and particularly Cuba. Of Spain's once vast American empire only Cuba and Puerto Rico remained after 1825. Essentially then, the story of the abolition of the slave trade within the Spanish colonial empire is the story of the abolition of the slave trade to Cuba.

Cuba was an ideal colony for Spain as long as she could hold it. As the wealth of her largest plantation colony grew, Spain was able to cover the cost of Cuba's administration and the expenses of Spanish military forces stationed there from Cuban revenues. Throughout the nineteenth century Cuba was a very important market for Spanish exports and the carrying trade between Spain and Cuba fostered the growth of a Spanish merchant marine. But Cuba's importance to Spain was much more than that of a self-supporting colony and trading partner for the metropolis.

The year 1861 was an unlikely one for optimistic predictions about a quick end to the Cuban slave trade. In 1859, and again two years later in 1861, more slave-trading expeditions set out for Africa than at any time since 1820 when the African slave trade had been declared illegal within the Spanish empire. British estimates of slave importations into Cuba during the three years 1859–61 were the highest in forty years; a total of 79,332 African slaves had been added to the Cuban slave population, thought to number 370,553 in 1861, and there was every expectation that the Cuban slave trade would carry on at the same high level. The open participation of American ships and capital, combined with improvements in maritime technology, had transformed the African slave trade. Large steamships were supplanting smaller sailing vessels as the main carriers of slaves. The number of slaves who could be transported in a single expedition rose dramatically. Two steamships alone accounted for 3,000, or approximately 10% of the slaves introduced into Cuba in 1859; one steam vessel in 1860 brought a cargo of 1,500 African slaves.

Technological improvements also were transforming the Cuban sugar economy, increasing its productive capacity and aggravating the labour shortage which the planters traditionally had resolved through the slave trade. Cuba's sugar estates had expanded rapidly in both number and size during the middle years of the nineteenth century, an expansion which the adaptation of steam power had accelerated.

The apparent success of British pressure against the foreign slave trade in 1845, with the passage of the Aberdeen Act (giving Britain unilateral powers to attack the slave trade to Brazil) and the Spanish penal law, masked the crisis over British abolitionist policy which was coming rapidly to a head. The campaign for free trade in Britain had divided the abolitionists among themselves, with the majority joining in an uncomfortable alliance with West Indian merchants and planters and protectionists in Britain in a vain effort to keep out slave-grown sugar. Even before the victory of free trade, abolitionists and some free traders had challenged the naval blockade system off West Africa, the cornerstone of British slave trade suppression. With free trade triumphant, the movement to do away with the cruisers gathered public momentum and by 1848 the defenders of the use of force feared their policy would be swept away just as protection had been. Where in 1840 the British abolitionist movement exercised a powerful influence on government policy, by 1850 the divisions over free trade and the use of naval force noticeably reduced the effectiveness of British abolitionist pressure.

During the same period the British government, facing the growing militancy of American expansionism and with the United States acquisition of Cuba an ever present danger, discovered that its freedom to act against the Cuban slave trade had narrowed considerably. Britain had to be much more circumspect towards Cuba than she had been before and more so than she was towards Brazil.

The celebration of the end of apprenticeship in the British Caribbean colonies in 1838 was a triumphal acknowledgement by British abolitionist leaders that their long campaign against slavery in the British empire was over. This great success encouraged them to set their sights on much larger targets, the foreign slave trade and foreign slavery. The goal now was to abolish slavery all over the world. The United States, naturally, was the main culprit in the Americas, closely followed by Brazil and Cuba where the slave trade still flourished in spite of treaties outlawing it.

Led by the Quaker businessman, Joseph Sturge, the abolitionists in Britain organized the British and Foreign Anti-Slavery Society in 1839, believing that a new and efficient organization was a necessary prerequisite if the movement was to accomplish its world-wide aim. The international emphasis of the British and Foreign Anti-Slavery Society was only natural since the battle had been won in the British empire, but it implied changed tactics. Pressure on the British Parliament could at best have an indirect effect on the foreign slave trade and on foreign slavery. The focus would have to be on world opinion and, to some extent, away from direct political action. Given the dominance of Quakers in the Society–nearly half the members of the governing committee in the first thirty years of the Society's existence were Quakers – the strong pacifist convictions of this resurgent abolitionist movement should not be surprising.

In the treaty she signed with Britain in 1835, Spain contracted to pass legislation to end the African slave trade to her Caribbean colonies. Britain, as the other party to the treaty, had a natural interest in ensuring the fulfilment of Spain's contract. When it became clear as early as 1836 that the Havana authorities had succeeded in blunting the impact of the new treaty in Cuba, what had been originally a subsidiary part of the main structure of slave trade suppression now became, in British eyes, at least as important as the treaty itself. Spanish co-operation was imperative if the slave trade to Cuba was to be stopped. The passage of Spanish legislation would be a tangible demonstration of this co-operation and a definite signal to the Cuban planters that the metropolis was determined to stamp out the slave trade. Little did the British government realize when it reminded Spain of her obligation to promulgate a penal law, two months after the ratification of the treaty, that nine more years would pass before the law would finally appear and that its provisions actually would protect instead of prosecute the slave traders of Cuba.

After the British reminder, an investigation, ordered by the Spanish Foreign Minister, discovered that steps had indeed been taken to fulfil Spain's contracted promise. Civil servants had drafted a law which had been laid before the upper chamber of the Spanish Parliament in December 1835. A commission of three distinguished Spanish jurists, headed by Martínez de la Rosa who had negotiated and signed the slave trade treaty for Spain, had gone over the draft proposal before it went to the legislature.