Simplify the following text for a Grade 10 native English-speaking person.
Original: After Cao Cao 's death in 220 , Cao Pi forced Emperor Xian to yield the throne to him , ending the Han Dynasty and establishing the Cao Wei kingdom . Sun did not immediately submit to Cao Wei or declare independence after Cao Pi 's enthronement , but took a wait-and-see attitude ; by contrast , in early 221 , Liu Bei declared himself emperor , establishing Shu Han .
Simplified: After Cao Cao 's son Cao Pi started the Wei Dynasty in 220 , Liu Bei also wanted to be an emperor and declared himself Emperor of Shu Han in 221 .