They were driven out by Boer trekkers in 1837.
The British government thought otherwise; they held that the trekkers could not divest themselves of their allegiance to the Crown.
The Great Trek, as it is called, lasted from 1836 to 1840, the trekkers, who numbered about 7000, founding communities with a republican form of government beyond the Orange and Vaal rivers, and in Natal, where they had been preceded, however, by British emigrants.
These, then, were the direct causes of the voluntary expatriation of the majority of the first trekkers, who included some of the best families in the colony, but they fail to explain the profound hostility to Great Britain which thereafter animated many, but not all, of the emigrants, nor do they account for the easy abandonment of their homes by numbers of the trekkers.
It intensified in the minds of many Boers the feeling of hostility towards the British already existing; some of the trekkers in1836-1840had taken part in and others had passively aided the rebellion of 1815 - " the most insane attempt ever made by a set of men to wage war against their sovereign " (Cloete, op. cit.
Summing up, it may be said that the exasperation caused by just grievances unremedied was no stronger a motive with the trekkers than the desire to be free from the restraints imposed on British subjects and the wish to be able to deal with the natives after their own fashion.
The trekkers had been told by the lieutenant-governor of the eastern province (Sir Andries Stockenstrom) that he was not aware of any law which prevented any British subject from settling in another country, and in the words of Piet Retief's declaration they quitted the colony "under the full assurance that the English government has nothing more to require of us, and will allow us to govern ourselves without its interference in future."
Other trekkers followed in the wake of Retief, and attacking Dingaan avenged the massacre.
Made effective their contention that the trekkers were still British subjects.