Complex sentence: In 1836 he had established a local newspaper in Taunton, the Somerset County Gazette in Taunton, but sold the title, when he moved to London to pursue his career as a barrister.
Split into simpler sentences: In 1836 he had established a local newspaper in Taunton, the "Somerset County Gazette", but sold the title. Cox moved to London to pursue his career as a barrister.