Simplify the following text for a Grade 11 native English-speaking person.
Original: Because much of medieval Europe lacked central authority to provide protection , such as a police force ( to use a modern analogy ) , each city had to provide its own protection for citizens both inside the city walls , and outside .
Simplified: Because much of medieval Europe lacked central authority to provide protection , each city had to provide its own protection for citizens both inside the city walls , and outside .