The Voortrekkers were a group of frontiersmen who trekked east into the South African inland to escape the British rule in the Cape. The British forced the Dutch in the conquered Cape to speak English in their churches, and many of the Dutch saw the British enlightenment power as an affront to their religion and their culture. So they moved inland to become self-governing, and the movement became known as 'The Great Trek'; a mass exodus from the British controlled Cape Colony.
At the same time, however, the Zulu Kingdom was moving south westward, so that both forces met in what had been empty land. The Zulu's resulting treachery when they murdered Piet Retief led to the Battle of Blood River in 1838 when God granted the Boers (the Voortrekkers) an overwhelming victory.