Complex sentence: Serious philatelic research and collecting, up to the early 20th century, was generally regarded as a field for "men only" to enjoy, and Louise Dale was prominent in breaking this cultural mold, and establishing women in the ranks of philately.
Split into simpler sentences: Serious philatelic research and collecting, up to the early 20th century, was generally regarded as a field for "men only" to enjoy. Louise Boyd Dale was prominent in breaking this cultural mold, and establishing women in the ranks of philately.