Complex sentence: The Communist Party never again held such a strong position in the union movement, nevertheless the issue remained potent and in 1955 the Democratic Labor Party was formed by disaffected ALP members who were concerned over communist influence in some Australian unions.
Split into simpler sentences: The Communist Party never again held such a strong position in the union movement. The issue of communist influence in the unions remained potent and led to the Australian Labor Party split of 1955 and the formation of the Democratic Labor Party comprising disaffected ALP members who were concerned over communist influence in Australian unions.