Complex sentence: Joplin is likely to have first lived in Sedalia as a teenager before moving to St. Louis, so he would have known the town which in the 1890s had a population of approximately 14,000 and was the centre of commerce and transport for the region.
Split into simpler sentences: Joplin is likely to have first lived in Sedalia as a teenager before moving to St. Louis, so he would have known the town. In the 1890s Sedalia was a town of about 14,000 and the centre of commerce and transport for the region.