Complex sentence: All spectator sports in the United Kingdom experienced a surge in interest in the years following the end of World War II. Rugby league was no different, and large crowds came to be expected as the norm for a period of around 20 years.
Split into simpler sentences: All spectator sports in the United Kingdom experienced a surge in interest in the years following the end of World War II and rugby league boomed. Large crowds came to be expected as the norm for a period of around 20 years.