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.

From the middle of the eighteenth century Cuba began to experience the remarkable economic growth which was to transform the island from a relative backwater of Spain's colonial empire into the world's richest colony and leading sugar producer by the late 1820s. Cuba's importance to Spain hitherto had arisen chiefly from the strategic geographical location of its main port and capital, Havana, the traditional rendezvous for Spanish treasure ships on their way back to the peninsula. Prior to 1763 Cuba's economy was a mixed agricultural one based on tobacco, sugar and cattle grazing. Cuba was not yet dependent on sugar as were the other major Caribbean islands, Jamaica, Barbados and St Domingue. Even in the 1750s, however, the seeds of the later sugar latifundia were germinating; in spite of a tobacco boom the number of sugar plantations was growing. Cuba's sugar revolution occurred in the years after 1763. The official export figures of sugar from Havana offer dramatic evidence of sugar's conquest of Cuba. A yearly average of 13,000 boxes of sugar left Havana in 1760–3, rising to 50,000 boxes in 1770–8 and to over 80,000 in 1778–96. Yearly averages from 1796 to 1800, amounting to nearly 135,000 boxes a year, illustrate how well Cuba capitalized on the vacuum created by the devastation of St Domingue.

The French colony of St Domingue had been the leading sugar producer in the Caribbean prior to the French Revolution, but the Revolution in 1789 set off a series of slave rebellions in the island which escalated into civil and race war, destroying the island's economy but leading eventually to the creation of Haiti, the first independent, black republic in the Caribbean.

Early in the struggle to abolish the British slave trade, the leading abolitionists realized that to make any abolition effective it would have to be universal. Another reason for seeking foreign co-operation was to undermine the domestic opposition argument that Britain's maritime rivals would be the chief beneficiaries of a British abolition. In December 1787 the Prime Minister, William Pitt, himself an advocate of abolition, wrote to William Eden, then Minister in Paris and Minister-designate to Madrid, referring to the abolitionist crusade, ‘if you see any chance of success in France, I hope you will lay your ground as soon as possible with a view to Spain also’.

The Parliamentary leader of the abolitionists, William Wilberforce, initiated several other attempts to obtain international agreement on the prohibition of the slave trade during the next twenty years, but the French Revolution, the revolution in St Domingue and the Napoleonic Wars dashed any hopes of success just as they acted to frustrate the abolitionist campaign within Britain. Wilberforce never lost an opportunity to press for international action, especially prior to the peace negotiations leading to the Treaty of Amiens in 1802, but the failure of these tentative overtures accentuated the importance of the struggle in Britain. British abolitionists were morally certain other nations would follow Britain's lead if only Britain would set the example. Henry Brougham confessed:

We have been the chief traders, I mean, the ringleaders in the crime.

Conflicting approaches to the implementation of the treaty, 1817—24

Two dilemmas faced the Cuban government when copies of the slave trade treaty arrived in Havana in February 1818. Genuine administrative difficulties were involved if the treaty was to be implemented. Ramírez, the Intendant of Havana, wanted to know which tribunals were to be responsible for judging cases of illegal slave trading not covered by the provisions of the treaty, specifically in connection with slavers arriving in Cuban ports after eluding capture at sea. It was clear that a contraband trade would continue and Ramírez advocated the merits of using the courts under his jurisdiction, suggesting that they be authorized to enforce the royal cédula of the previous December. The Council of the Indies ruled against the Intendant in a report to the King of 11 May 1819, in which it assigned overall responsibility for the implementation of the treaty to the Captain-General.

Far more serious were the apprehensions of Cuban planters and merchants who foresaw a catastrophe for Cuba if the treaty was fully implemented. The catastrophe they feared was economic, although there were other dangers as well. Even the publication of the royal cédula was resisted on the grounds that it might set off a chain reaction among the slaves. The Captain-General was forced to adopt a compromise formula, publishing the cédula only in the newspapers of Havana, and communicating it to the rest of the island through the various lieutenant-governors. At first the merchant and planter groups in Cuba expressed their opposition tentatively.

The Congress of Vienna and Spanish abolition

After Britain's behind-the-scenes role in the Cortes debate of 1811, the British government took no further diplomatic action to persuade Spain to abolish the slave trade until 1814. By then the war was over and British abolitionists were leading a feverish agitation against the slave trade. Their chief aim in the spring of 1814 was to persuade the European powers to agree on a convention to prohibit the slave trade. In a letter to James Stephen on 18 April, Wilberforce summed up his attitude to the Spanish and Portuguese slave trade: ‘It happens quite providentially that the only powers which are interested in carrying the Slave Trade on, are Spain and Portugal, and they may surely be compelled into assent.’

The campaign focussed on the task of preventing the revival of the French slave trade. When the abolitionists discovered that in the treaty of peace with France all France's colonies were returned to her in exchange for a promise to give up the slave trade in five years, they were bitterly disappointed. Redoubling their efforts, they roused public opinion in the country and were the instrumental force behind the overwhelming flow of petitions to the House of Commons which protested against the revival of the French slave trade. In thirty-four days beginning 27 June 1814, the House of Commons received 772 petitions with nearly one million signatures. As Webster says, ‘the subject was one in which almost the whole nation had become interested. It could not be ignored’.

The abolition of slavery within the British empire in 1833 had a revolutionary impact on Britain's West Indian colonies, but the Caribbean effects of British humanitarianism were not confined to British colonies. The influence of British abolitionist ideas and subsequently of British abolitionists themselves spread quickly from Jamaica to Cuba, the nearest and largest of the remaining slave plantation colonies of the Caribbean. Cuban planters and Spanish colonial officials knew only too well that it had been British pressure on Spain to abolish the slave trade, after Britain herself had prohibited it, which had led to the Anglo-Spanish treaties of 1817 and 1835, prohibiting the slave trade to Cuba; the abolition of slavery within British colonial possessions portended a similar campaign to eliminate slavery in Cuba. Within Cuba abolitionism was viewed as a foreign import which, in the eyes of the European planter class and Spanish officials, was a foreign menace. In an ironic and unwitting interaction of British colonial and foreign policy, the emancipation of slaves in the British West Indies provoked a greater reaction in Cuba than the long and persistent effort of British officials to stop the Cuban slave trade.

The Cuban government, supported every step of the way from Madrid, took all possible precautions to prevent abolitionist ideas from seeping into the island. Beginning in the late 1820s as the campaign against slavery in the British empire began to gather force, Cuban authorities enacted a series of measures designed to guard the island against this intangible enemy.

Force was not one of the weapons in Britain's diplomatic bag of pressures to secure Spain's prohibition of the slave trade. At the same time the British government was not prepared to tolerate the evasion of British laws against slave-trading, either by British subjects engaging in the foreign slave trade or by foreigners smuggling slaves into British possessions.

Two cases, one before the Privy Council and one before the High Court of Admiralty in 1811, showed how far courts would support officers enforcing British laws. In the first, the case of the Amedie, a United States ship believed to be engaged in the slave trade to Cuba, it was stated that since the slave trade had been totally prohibited by Parliament, and pronounced contrary to the principles of justice and humanity, prima facie the trade was illegal. It was then up to the claimants to prove by their own laws, assuming they were not British, the trade was not prohibited.

This principle was used as a weapon against United States participation in the Atlantic slave trade. In a later case the Amedie judgement was interpreted as saying: ‘that the slave trade carried on by a vessel belonging to a subject of the United States is a trade which, being unprotected by the domestic regulations of their Legislature and Government, subjects the vessels engaged in it to a sentence of condemnation.’

When the Duke of Infantado informed the British Minister in Madrid of the royal order of 1826, he asked Lamb if the British government could suggest any other measure which would help to suppress the slave trade. Canning responded to this opening with a proposal that Spain follow Holland's example and sign an equipment article which would then mean that suspected Spanish slavers, equipped to carry on the slave trade, could be seized and condemned even if they did not have slaves on board. This proposal was made official in a Note addressed to the Spanish Foreign Minister on 19 February 1826. The suggestion was then turned over to the Council of the Indies for study. Their report was quite favourable. The Council did not find any objection to the additional article, although it felt more ought to be done to make the existing laws effective. Should the equipment article be approved, the Council recommended a six-month period of grace to date from the publication of the new article, and it believed that the punishment for infractions should be limited to the confiscation of the ship and its cargo.

Ferdinand referred the report to his Council of State which, in turn, asked the Spanish Foreign Minister for his opinion; however, before the Duke of Infantado had a chance to examine the problem he was replaced as Foreign Minister. A Foreign Ministry memorandum succinctly describes what happened next: ‘here the affair remained paralysed’.

Spain enacted the penal law of 2 March 1845 to fulfil her treaty obligations with Britain. For over twenty years it remained the only law under which Spanish officials in Cuba worked to suppress the slave trade. Not until February 1866 did a more extensive law, designed to replace the 1845 legislation, first appear in the Spanish Senate and another year passed before it received legislative sanction. The preamble of the 1866 bill admitted the inadequacies of its predecessor, a long overdue public acknowledgement of the obvious. For years, successive Captains-General had been saying the same thing in stronger terms contained in confidential despatches and letters to the peninsular government; even Spanish legal officials in Cuba, who earlier had defended the law, by the late 1850s and 1860s recognized its shortcomings. The British commissioners in Cuba and through them the British government had been the first to see what was later apparent to all; the 1845 penal law was a failure. Far from aiding in the suppression of the Cuban slave trade, the law actually encouraged what it was meant to stop.

Captain-General O'Donnell acknowledged receipt of the royal orders accompanying the penal law in a confidential despatch dated 15 February 1845. He warned of the grim prospects for Cuba if the enforcement of the law succeeded in cutting off the flow of slaves to the island. With the ratio of female to male slaves at 1:5, there was no possibility that natural reproduction would make up for the estimated 5% annual mortality among the plantation slaves.