The abolitionist Thomas Clarkson had an enormous influence on Wilberforce. He and others were campaigning for an end to the trade in which British ships were carrying black slaves from Africa, in terrible conditions, to the West Indies as goods to be bought and sold. Wilberforce was persuaded to lobby for the abolition of the slave trade and for 18 years he regularly introduced anti-slavery motions in parliament. The campaign was supported by many members of the Clapham Sect and other abolitionists who raised public awareness of their cause with pamphlets, books, rallies and petitions. In 1807, the slave trade was finally abolished, but this did not free those who were already slaves. It was not until 1833 that an act was passed giving freedom to all slaves in the British empire.