The oral traditions of all the Nilotic peoples of East Africa refer to northern origins. There is a consensus among historians and linguists that the Plains and Highland Nilotes migrated from a region near the southern border of Ethiopia and Sudan shortly before the beginning of the Christian Era and diverged into separate communities shortly thereafter. Ehret (1971) believes that pre-Kalenjin who already were cattle keepers and had age sets lived in the western Kenya highlands 2,000 years ago. Presumably, these people absorbed other populations already living in the region. From some time after A . D . 500 to about A . D . 1600, there seems to have been a series of migrations eastward and southward from near Mount Elgon. Migrations were complex, and there are competing theories about their details.
The Nandi and Kipsigis, in response to Maasai expansion, borrowed from the Maasai some of the traits that distinguish them from other Kalenjin: large-scale economic dependence on herding, military organization and aggressive cattle raiding, and centralized religious-political leadership. The family that established the office of orkoiyot (warlord/diviner) among both the Nandi and Kipsigis were nineteenth-century Maasai immigrants. By 1800, both the Nandi and Kipsigis were expanding at the expense of the Maasai. This process was halted in 1905 by the imposition of British colonial rule.
Introduced during the colonial era were new crops/techniques and a cash economy (Kalenjin men were paid wages for their military service as early as World War I); conversions to Christianity began (Kalenjin was the first East African vernacular to have a translation of the Bible). Consciousness of a common Kalenjin identity emerged to facilitate action as a political-interest group during and after World War II—historically, the Nandi and Kipsigis raided other Kalenjin as well as the Maasai, Gusii, Luyia, and Luo. The name "Kalenjin" is said to derive from a radio broadcaster who often used the phrase (meaning "I tell you"). Similarly, "Sabaot" is a modern term used to mean those Kalenjin subgroups who use "Subai" as a greeting. Nandi and Kipsigis were early recipients of individual land titles (1954), with large holdings by African standards because of their historically low population density. Economic development schemes were promoted as independence (1964) approached, and afterward many Kalenjin from more crowded areas resettled on farms in the former White Highlands near Kitale. Today's Kalenjin are among the most prosperous of Kenya's ethnic groups. Kenya's second president, Daniel arap Moi, is a Tugen.