Complex sentence: By the end of the year approximately 27,000 South Africans were serving in East Africa, in either the 1st South African Division, the 11th African Division, or the 12th African Division.
Split into simpler sentences: By the end of the year, approximately 27,000 South Africans were serving in East Africa. The South Africans were either in the 1st South African Division, the 11th African Division, or 12th African Division.