The Map of WW1 in East Africa produced by Mehmet Berker (2008) gives a very detailed graphical summary of events in this period. The map is reproduced below for convenience and the full wikipedia entry can be found here. The online version of the map may be zoomed to show the detailed information more clearly.
All credit to Mehmet Berker for producing this excellent resource and sharing it publicly for the benefit of those interested in events in East Africa during WW1. Highly valuable.