Simplify the following text for a Grade 7 native English-speaking person.
Original: The county was significantly affected by the expansion of the metropolitan area of London in both the 18th and 19th centuries , such that from 1855 the south-east was administered as part of the metropolis .
Simplified: The county was affected by the expansion of London in the 18th and 19th centuries . From 1855 the south east was administered as part of London .