Migrations and invasions were motivated by the search of new pastures and more fertile lands, as well as by the wish to seize the wealth of the neighbouring tribes, their cattle and their women. The attacked tribes fled to quieter territories, subsequently obliging other settlers to move farther beyond. Over the centuries, the different tribes established commercial relationships and alliances to cope with the drought periods.

Until the 16th century, several ethnic groups inhabited the Bantu areas from Eastern Uganda to Lake Victoria. The south of the lake and the Nyanza province were populated by the Kisii. From the year 1500, the Luos started to invade the northeastern flank of the lake. Some resident tribes were integrated by the new settlers, but others were pushed northwards and eastwards, taking the Buluyia land and grouping together in what we now know as the Luyha people. The Kisii, pressed by the Luos and by the wars of Maasais and Kipsigis, migrated northwards to their current lands in Kisii Hills.

In Eastern Kenya, the entry of the Somalis, northern Cushites coming from the Horn of Africa and possibly natives of Arabia, displaced the Boran and Galla people, also Cushites. Borans moved to the region of Wajir, while the Gallas' migration eastward pushed the Eastern Bantu groups, located at the north coast, southwards and westwards. The Mijikendas settled south of Malindi, whilst Kikuyus and Embus moved inland following the Tana river.

Along the 19th century, the Kambas started to arrange caravans carrying ivory from the inner lands to the coastal trade centers. Meanwhile, in the western regions, the Nandis took advantage of the Maasais' weakness to become the most powerful group in the area at the end of the century, dominating the Luyhas and Luos, right at the time when the white men were launching their expeditions to the unspoiled lands of inner Kenya.