Complex sentence: He became shadow Attorney-General under the leadership of Frank Wilkes, but when Wilkes lost the 1979 election to the Liberal premier, Dick Hamer, Cain challenged him for the leadership, becoming leader in September 1981.
Split into simpler sentences: He became shadow Attorney-General under the leadership of Frank Wilkes. After Wilkes narrowly lost the 1979 election to the Liberal premier, Dick Hamer, Cain challenged him for the leadership, becoming leader in September 1981.