Complex sentence: In 1980, the former anarchists of the Libertarian Communist Group joined Big Flame, but as more members of the group defected to the Labour Party, the group was wound up in about 1983.
Split into simpler sentences: In 1980, the former anarchists of the Libertarian Communist Group joined Big Flame. However, as more members of the group defected to the Labour Party, the group was wound up in about 1983.