Simplify the following text for a Grade 5 native English-speaking person.
Original: According to The Institute for Research on World-Systems , Kamakura was the 4th largest city in the world in 1250 AD , with 200,000 people , and Japan 's largest , eclipsing Kyoto by 1200 AD .
Simplified: In 1250 , Kamakura was the 4th largest city in the world with 200,000 people .