Complex sentence: These closely follow the pattern of the 1833 territorial division of Spain; the only major change of provincial borders since that time has been the division of the Canary Islands into two provinces rather than one.
Split into simpler sentences: These closely follow the pattern of the territorial division of the country carried out in 1833. The only major change of provincial borders since that time has been the sub-division of the Canary Islands into two provinces rather than one.