The second inhabitants of the region who came in a great migration and founded kingdoms across the region

The correct answer is the Bantu speaking peoples

The Bantu peoples, or the proto-Bantu speaking peoples, came from what is nowadays Cameroon and they spread across all of sub-saharan Africa in a series of migrations where they displaced the natives who lived there before. The two main migrations were from Cameroon towards South Africa, and another was from central Africa towards the north and the south.