Complex sentence: Committed Communists, the Lerners were involved in numerous grassroots activities involving trade unionism, civil rights, and anti-militarism; they struggled against McCarthyism, especially the Hollywood blacklist.
Split into simpler sentences: Committed Communists, the Lerners were involved in numerous party activities involving trade unionism, civil rights, and anti-militarism. They struggled against McCarthyism, especially the Hollywood blacklist.