The slave trade ended in Britain in 1807, when authorities agreed with the growing number of abolitionists (those who argued that slavery is immoral and violates Christian beliefs) and outlawed the trade. In 1833 slavery was abolished throughout the British colonies as the culmination of the great antislavery movement in Great Britain. In the United States, the slave trade was prohibited in 1808, but possessing slaves was still legal. Consequently, trade on the black market continued until Britain stepped up its enforcement of its antislavery law by conducting naval blockades and surprise raids off the African coast, effectively closing the trade. The slave trade as it had been known officially came to an end after 1870, when it was outlawed throughout the Americas. Throughout the world, the United Nations works to abolish slavery and other systems of forced labor.