It was the British government that began the abolition of the slave trade during the years,1822 - 1826 . This was because of the pressure by various groups based on different factors;
Rise of humanitarians in Europe such as Christians and scholars condemned it on moral grounds. The missionaries wanted it to be stopped because they wanted good conditions for the spread of Christianity. The formation of the humanitarian movements in England aimed at stopping all kinds of cruelty including slave trade, flogging of soldiers and child labour.
Industrialization in Britain was one of the main forces behind the abolition .E.g. Britain industrialists urged its abolition because they wanted Africans to be left in Africa so that Africa can be a source of raw materials for their industries, market for European manufactured goods and a place for new investment of surplus capital.
Formation of Anti-slavery movement and the abolitionist movement in 1787. Its chairman was Granville Sharp and others like Thomas Clarkson, William Wilberforce who gathered facts and stories about the brutality of slave trade and slavery to arouse public opinion in Britain.
Religious revival in Europe, Anglicans preached and condemned slave trade as being opposed to laws of God and humanity. Catholic popes also protested against the trade and prohibited it. In 1774, many religious leaders served as examples when they liberated their slaves in England.
The French revolution of 1789 and the American revolution of 1776 emphasized liberty, equality and fraternity(brotherhood) of all human beings. As a result, people began to question whether anyone had a right to deprive fellow man of his liberty when he had done wrong.
The British desire to protect their national interests, British planters wanted slave trade stopped to avoid competition with other European planters .This is because other planters were producing cheaper sugar ,British sugar accumulated hence the need to stop over production.
The rise of men with new ideas e.g. Prof. Adam Smith(challenged the economic arguments which were the basis of slave trade when he argued convincingly that hired labour is cheaper and more productive than slave labour, Rousseau spread the idea of personal liberty and equality of all men.
Slaves had become less profitable and yet had led to over population in Europe.
Influential abolitionists like William Wilberforce( a British member of parliament ) urged the British government to legislate against the slave trade in her colonies.
The ship owners stopped transporting slaves from Africa and began transporting raw materials directly from Africa and America to Europe ,which led to a decline in slave trade.