How did slave trade lead to the Great Trek?

The Great Trek (Afrikaans: Die Groot Trek; Dutch: De Grote Trek), starting in 1836 in southern Africa, was a mass migration of Dutch-speaking inhabitants of the British-run Cape Colony, who left the Cape and travelled eastward by wagon train, into the interior of the continent, in order to live beyond the reach of the British colonial administration. Both the Cape Colony and the area newly settled by the migrants later became part of what is today the country of South Africa.[1] The Great Trek was spurred by rising tensions between rural descendants of the Cape's original, mostly Dutch, European settlers, known collectively as Boers, and the later, mostly British, settlers, who had taken control of the Cape on behalf of the British Empire.[2] It was also spurred by an increasing yearning among members of the various Boer communities to live in a more isolationist, semi-nomadic way than had become possible in Cape Town, which was becoming much more administratively complex under British management.[3] Boers who took part in the Great Trek identified themselves as voortrekkers, meaning "pioneers" or "pathfinders" (literally "fore-trekkers") in Dutch and Afrikaans.

The Great Trek led directly to the founding of several autonomous Boer republics, namely the South African Republic (also known simply as the Transvaal), the Orange Free State, and the Natalia Republic.[4] It was also responsible for the displacement of the Northern Ndebele people,[5] and was one of several decisive factors influencing the decline and collapse of the Zulu Kingdom.[3]