Complex sentence: In 1947, Marseilles was the main trading port of the French colonial empire and it had a communist mayor, Jean Christofol, who was backed by the trade unions, popular among longshoremen, transportation workers, and dockworkers.
Split into simpler sentences: In 1947, Marseilles had a communist mayor, Jean Christofol, who was backed by the trade unions. He was popular among longshoremen, transportation workers, and dockworkers.