The main reason it took so long to abolish the slave trade was simply because the pro-slave trade lobby had too many important and powerful figures in the establishment. The plantation owners, the merchants and those living in Britain, some of them MP’s, were well organised, as well as being powerful and wealthy enough to bribe other MPs to support them.
The Prime Minister William Pitt had been a supporter of abolition, but the war with France changed his views. During the war he did not want to upset the cabinet ministers that were mostly against abolition. Therefore he withdrew his support for the abolitionists. Additionally the events in St Domingue convinced Pitt that to abolish slavery would be a disaster.
King George III was against the abolition movement, as was his son, the Duke of Clarence. Support for abolition in Parliament was now restricted to the committed few.
The new Prime Minister, Lord Grenville actively promoted fellow abolitionists to cabinet. More MPs had committed themselves to abolition during the 1805 election campaign.
The Foreign Slave Trade Abolition Bill of 1806 represented a change of strategy. Rather than have Wilberforce represent yet another straightforward abolition bill, the parliamentary abolitionists secretly agreed to pretend to 'ignore' a Foreign Slave Trade Abolition Bill, which was instead sold as an anti-French measure to the House of Commons.
The Bill was designed to prevent British merchants from importing slaves into the territories of foreign powers.
It was only on the third reading of the Bill, that the pro-slavery lobby realised what was really at stake behind the Bill. It would have been difficult to oppose it because the Government presented it as a way to win the Napoleonic war.