British expansion into the Cape originated in global trade and sea-power motives.

Evidence

The British were drawn to the Cape initially to secure geopolitical sea power through control of the passage of global trade at the time. They soon found, like their Dutch predecessors, that the Cape was not simply a cartographic crossroads, a controlling point in the passage of global power. The Cape offered opportunities and challenges of its own, possibilities for local wealth generation, the provision of raw materials to fuel British industrial growth, and a site for expressing imperial power locally asserted. — David Theo Goldberg, The Threat of Race, 1399