By century’s end, abolitionism seemed to have reached something of an impasse on both sides of the Atlantic. But then in 1804 the British movement sprang back into life, presumably at the instigation of William Wilberforce. The government was clearly in favor of the measure. Furthermore, the entry into Parliament of a batch of new "liberal" Irish MPs, following the Act of Union of 1801, subtly altered the disposition of pro- and anti-slavery forces in the House of Commons.
By 1807 it also looked as though it would be possible to build an international coalition against the transatlantic slave trade, something that had proved impossible during the 1790s. Denmark had already abolished it in 1792. The United States was expected to follow suit in 1808, while for different reasons Holland, Portugal, and France were all highly susceptible to diplomatic pressure. Perhaps just as important, a modest increase in slave births over deaths in the British Caribbean, notably in Barbados, held out the prospect that the British sugar colonies might be able to supply themselves.
In this sense, the abolition of the slave trade was a pragmatic decision made in the knowledge that Britain could probably afford to dispense with it. Yet there is little doubt that public opinion was behind the measure, or that many MPs were swayed by the moral arguments put forward by Wilberforce and his supporters.
The death of William Pitt in 1806 also proved an important turning point. The new government, Lord Grenville’s "Ministry of All the Talents," was known to be in favor of the measure. In 1806 it brought in a bill prohibiting the slave trade to conquered Dutch Guiana. Seizing this opportunity, Wilberforce began to attach the provisions of his own Foreign Slave Bill to the proposed legislation. The Foreign Slave Bill was passed into law in 1806, paving the way for the Abolition Act of 1807, which finally outlawed all British involvement in the Atlantic slave trade. As predicted, a year later the United States also officially abandoned the slave trade, in accordance with the constitutional ban agreed to in 1787.