Complex sentence: A Nigerian brigade together with two East African brigades (KAR) and some South Africans, formed the 11th African Division whilst the 12th African Division was similarly formed but with a Ghanaian brigade instead of a Nigerian one.
Split into simpler sentences: A Nigerian brigade together with two East African brigades (the KAR brigades) and some South Africans, formed the 11th African Division. The 12th African Division was similarly formed but with a Ghanaian brigade instead of a Nigerian one.