Complex sentence: In 1972, Cordell began what is referred to by his readers as his second Welsh trilogy beginning with "The Fire People", set in Merthyr Tydfil against the background of the 1831 Merthyr Rising, for which Cordell did considerable research.
Split into simpler sentences: In 1972, Cordell wrote "The Fire People", set in Merthyr Tydfil. It is set against the background of the 1831 Merthyr Rising, for which Cordell did considerable research.