Complex sentence: South Wales suffered great economic and cultural turmoil in the early 20th century, this was reflected by a decline in the popularity of traditional Welsh pursuits such as Pêl-Llaw.
Split into simpler sentences: South Wales suffered great economic and cultural turmoil in the early 20th century. The changes and turmoil were reflected by a decline in the popularity of traditional Welsh pursuits such as Pêl-Llaw.