In 1805 the British House of Commons passed a bill that made it unlawful for any British subject to capture and transport slaves, but the measure was blocked by the House of Lords.
In 1806, Lord Grenville formed a Whig administration. Grenville and his Foreign Secretary, Charles Fox, were strong opponents of the slave trade. Fox and William Wilberforce led the campaign in the House of Commons, whereas Grenville, had the task of persuading the House of Lords to accept the measure.
Greenville made a passionate speech where he argued that the trade was "contrary to the principles of justice, humanity and sound policy" and criticised fellow members for "not having abolished the trade long ago". When the vote was taken the Abolition of the Slave Trade bill was passed in the House of Lords by 41 votes to 20. In the House of Commons it was carried by 114 to 15 and it become law on 25th March, 1807.
British captains who were caught continuing the trade were fined £100 for every slave found on board. However, this law did not stop the British slave trade. If slave-ships were in danger of being captured by the British navy, captains often reduced the fines they had to pay by ordering the slaves to be thrown into the sea.
Some people involved in the anti-slave trade campaign such as Thomas Clarkson and Thomas Fowell Buxton, argued that the only way to end the suffering of the slaves was to make slavery illegal. However, it was not until 1833 that Parliament passed the Slavery Abolition Act.
Un The US, Abraham Lincoln is credited for "freeing the slaves" with his Emancipation Proclamation in 1963, but the Proclamation was limited in many ways. It applied only to states that had seceded from the Union, leaving slavery untouched in the loyal border states. It also expressly exempted parts of the Confederacy that had already come under Northern control. Most important, the freedom it promised depended upon Union military victory.
The Proclamation was not a law passed by Congress but a presidential order empowered by Lincoln's position as Commander in Chief of the Army and Navy. As the Union armies conquered the south, thousands of slaves were freed each day until nearly all (estimated at 4 million) were free by July of 1865. Some slavery continued to exist in the border states until the entire institution was finally wiped out by the ratification of the Thirteenth Amendment in 1865.
Japan abolished slavery in 1588, Saudi Arabia in 1962, and Mauritania in 1981. Illegal slavery still continues.