The US wants to stop other countries from colonizing Africa so it will have the field open to itself. From Netfa Freeman at antiwar.com:
John Bolton’s recent unveiling of the Trump Administration’s “Prosper Africa” plan did what is typical of such U.S. foreign policy announcements. It performed the balancing act of admitting motives to protect vague “US interests” while dishonestly claiming benevolent intentions for the other country, region, or continent concerned. In this case the continent is Africa.
The “new” Africa policy, National Security Advisor Bolton suggested, is an adjusted US strategy to “assist” African economic independence from the predatory designs of China and Russia. In reality it is the Trump’s administration taking the baton from the Obama administration in the new Scramble for Africa, a sequel to the proliferation of conflicting European claims to African territory during the New Imperialism period, between the 1880s and the start of World War I.
Bolton admits as much when he calls the administration’s new plan a response to “predatory practices pursued by China and Russia [that] stunt economic growth in Africa; threaten the financial independence of African nations; inhibit opportunities for US investment; interfere with US military operations; and pose a significant threat to US national security interests.”
It should be obvious that Bolton cares little about predation – he just doesn’t want other predators to compete with. He made no mention of the US Africa Command (AFRICOM), which has put most African nations under the effective military control of the United States. AFRICOM is the re-colonization of Africa by the US, with thousands of US troops now stationed in some 30 African countries and dozens of US bases across Africa. The total estimated cost for AFRICOM in 2018 is $236.9 million.