Simplify the following text for a Grade 8 native English-speaking person.
Original: Guan was captured by Sun 's general LÃ 1\/4 Meng ; once captured , Sun Quan executed Guan Yu , Jing Province came under Sun 's control , and the Sun-Liu alliance ended . Sun nominally submitted to Cao and urged him to take the throne but Cao refused .
Simplified: In alliance with Cao Cao , Sun Quan 's general LÃ 1\/4 Meng captured Guan Yu in 219 and slayed him along with his son , Guan Ping .