Thompson left the Communist Party of Great Britain in 1956, the year of the Soviet Union's intervention in Hungary. In later life he referred to himself as a Thompsonist rather than a Marxist. His academic work continued to demonstrate a Marxist-oriented outlook on history. The class structure of societies continued to play a central role in his studies. No longer playing an active part in politics, he maintained an enthusiastic interest. He was strongly opposed to the Soviet handling of the Prague Spring, and criticised British policy in Northern Ireland, particularly sectarian violence.