In 208 A.D.,Ts'ao Ts'ao took the emperor Hsien Ti captive,and with the emperor under his control,named himself the prime minister of the imperial government.Then he led his army and navy south to attack the Wu Kingdom located southeast of the Yangtze River.Ts'ao Ts'ao annexed the warlord Liu Tsung's troops and prepared to defeat Liu Pei,the ruler of the Shu Kingdom located southeast of the river.He sent a letter to Sun Chuan,the ruler of the Wu Kingdom,challenging Sun to a battle.