Sounds more like defense than attack.
Kalenjin were only africans who didnt live in Manyattas or clustered fortiifed villages like the rest.
Kalenjin each family lived alone in a ridge or two.
The reason our self-defense system had no peers.
You attack one kalenjin - and all they need to do is raise a war cry - and within few minutes - thousands of troops would on you.
Apart from section of Maasai - who came with huge battalion- no tribe dared attacked Kalenjin.
Maasai-Kalenjin fights were fought in open with rules.
Kalenjin livehood revolved basically around stealing cattle. Women worked their small kitchen gardens. Men exclusively raided or planned raids. Some raids would happen 200 miles - that is 400km away. It took meticous plan to avoid being massacred in enemy territory or driving the cattle back.
The planning took months - of reconnaissance and intelligence gathering - spies gathered information - hidding in enemy and studying the lay of the land. The actual attack would be swift - less than an hour. It had to happen at worst time of the night - because warriors needed to get a little advantage - otherwise you'd be finished.
By the time you the enemy or victim was raising their alarm or war cry - warriors would be gone...having covered significant distance.
Merus did what was a necessity to them,Merus are just 2M now precolonial period Merus might have just been 80k. Meru need not walk that far the only proper threat came from Samburu,Borana and Somali. They are the ones that did the walking Merus just stayed pretty and ambushed them along the way just exactly like what Ukrainians are doing to Russia,this kinds of battle are very demoralising and devastating to attacking forces. I think Kalenjins didn't face an enemy like the Meru who would just sit and watch your movements then pounce on you when you least expect.
Merus attacked during rainy season because of 2 reasons:
1) Farming communities could be ambushed in the farms and easily overwhelmed as they cultivated or planted the lands
2). Pastoralists communities whould be ambushed in the long thick grass and bushes as they grazed their cattle/camels.
This especially made the latter think of Merus as savages and primitive to this day.