Complex sentence: The Johnson Gang is the collective name for a group of English criminals from Cheltenham, Gloucestershire who specialised in stealing fine art and antiques from English country houses over a period of 20 years.
Split into simpler sentences: The Johnson Gang is the collective name for a group of English criminals, from Cheltenham, Gloucestershire. Who specialised in stealing fine art and antiques from English country houses over a period of 20 years.