Complex sentence: He was a longstanding member of the Southern Rhodesia Legislative Assembly, although his career was interrupted by other posts and by illness; as an ally of Sir Roy Welensky, he was Prime Minister of Southern Rhodesia from 1958 to 1962.
Split into simpler sentences: He was a longstanding member of the Southern Rhodesia Legislative Assembly, although his career was interrupted by other posts and by illness. As an ally of Sir Roy Welensky, he was Prime Minister of Southern Rhodesia from 1958 to 1962.