Complex sentence: He soon travelled back to Siam, but became involved in a succession war following the death of the King Songtham by Prasat Thong who had acted as "king-maker" before assuming the throne, by performing the double regicide of King Songtham's sons.
Split into simpler sentences: He soon travelled back to Siam, but became involved in a succession war following the death of the King Songtham by Prasat Thong. Presat Thong had acted as "king-maker" before assuming the throne, by performing the double regicide of King Songtham's sons.