Simplify the following text for a Grade 10 native English-speaking person.
Original: The district was formed in 1974 as the Metropolitan Borough of Sunderland as part of the provisions of the Local Government Act 1972 and is an amalgamation of four former local government districts of County Durham .
Simplified: The district was created in 1974 as the Metropolitan Borough of Sunderland when all local government in England and Wales was changed by the Local Government Act 1972 . This was when four different local government districts from County Durham were joined together .