The British colonies in East Africa were:

Kenya;
Uganda;
Nyasaland (now known as Malawi);
Northern Rhodesia (now known as Zambia).

As a result of the Great War, the former German colony of Tanganyika also became a British colony.

The King’s African Rifles were raised in 1902 from the various colonial regiments in British East Africa, to be the single regiment of the British Army covering these four (later five) countries. The regiment was funded by the colonial governments, with the main role of the troops to act as imperial police maintaining law and order in East Africa. The officers were all British, seconded from their parent regiments for colonial service.

After the Great War, the King’s African Rifles was reduced to six operational battalions. Each was under full strength, and were tasked with internal security. There were no artillery, engineer, or support services in East Africa. Budget constraints meant that rearmament was a slow process, and only really developed with the outbreak of the Second World War in September 1939. With the entry of Italy into the war in June 1940, this produced an immediate threat to Kenya, as an invasion of the Northern Frontier District was expected. In the end, a series of skirmishes was all that resulted until the main campaign was launched in January 1941.

This period allowed reinforcements to reach East Africa and for the raising of additional infantry battalions, together with supporting arms and services.