Complex sentence: Thornton was incorporated into the city of Bradford in 1899 and has been within the boundaries of the City of Bradford metropolitan borough since 1974, in which it comprises part of the Thornton and Allerton ward.
Split into simpler sentences: Thornton was incorporated into the city of Bradford in 1899. Thornton has been within the boundaries of the City of Bradford metropolitan borough since 1974, in which it comprises part of the Thornton and Allerton ward.