I found this theory(not proven) interesting, I always knew Somalis below the river and Somalis above the river are not the same culture, thinking, politics. Is it possible due to climate like the above video promotes that cultures and groups are formed by societies who share a common climate and therefore will have a common identity? Desert People, Forest people, mountain people, grass land people is the climate zones of Africa as a whole. What this doesn't explain is why are the south not united? or the north not united? if climate is the reason? it also said due to the various climate it created small groups and these small groups wouldn't combine into one force or community as they had strict borders and considered each other different communities as they don't live in the same environment nor speak the same language.