When Cao Cao died in 220, his son Cao Pi forced Emperor Xian of Han to give up his power. Cao Pi declared himself Emperor of the Wei Dynasty. Liu Bei found that offensive, for he was a member of the royal family of Han and considered himself the righteous Emperor of China. That's why he declared himself emperor of the Shu Han in 221. The next year, Sun Quan claimed the title "Emperor of Wu" for himself.