To avoid breaking the 20-year rule, I haven't provided reference to any ongoing political processes within the question. However, this was raised for me due to an ongoing process which I imagine most readers are not aware of- I certainly wasn't. As such, to promote the knowledge of political processes from other, often neglected areas of the world, I would like to provide this link to further information, which provides the present-day context for my question. I hope this slight flouting of rule 4 is acceptable to the mod team, so long as any further discussion is kept only to the historical record :)
I talked a little bit about efforts like the Federation of Mali and the Union of African States in this thread. Federation of Mali represented an attempt by two French colonies to enter independence as a federation, where the Union of African States was an effort by ex French colonies (Mali, Guinea) and an ex-british colony (Ghana) to form a federation.
Since you specified East Africa, I will hasten to mention that Tanzania qualifies as a federation. The official name of the country is the United Republic of Tanzania. Tanganyika (the mainland) gained independence in 1963, and Zanzibar had been a separate arab sultanate under British protectorate until the Zanzibar revolution in January 1964. After the Zanzibar revolution, the leader of the revolutionaries John Okello negotiated federation of Zanzibar with Tanganyika to form Tanzania.