Why did Qin give Hanzhong back to Chu?

At that time, Qin wanted to attack Yiyang, South Korea, fearing that Chu would help South Korea.

After the war in Danyang, Qin tried to win the favor of Chu by using its own skills and alienate the relationship between Chu and other six countries.

"Historical Records Chu Family" has such a record: "Next year, Qin will cut the land of Hanzhong and make peace with Chu."

In other words, Qin returned a piece of land, hoping to make peace with Chu again.

As a result, Chu Huaiwang not only resolutely refused, but also wanted to avenge himself.

Although Qin Wuwang went back on his word, Zhao Xiang, the king of Qin, returned Shang Yong (now southwest of Zhushan, Hubei) to Chu in order to ease the relationship with Chu. In order to seize Yiyang fortress, Qin made great concessions to its old enemy in the south.

Chu appeared in Yiyang battlefield.

Yiyang city is condescending, easy to defend but difficult to attack. South Korea sent heavy troops to help, and Qin Jun's attack was more difficult. In order to completely repel the attack of Qin, South Korea turned to Chu for help, and Chu Huaiwang also sent general Cui Jing to rescue Yiyang. On the occasion of the decisive battle between the Han and Qin armies in Yiyang City, an army of Chu suddenly went north, stationed at the foot of the mountain near Yiyang City, sitting quietly and watching the tigers pounce!

Qin Wuwang was shocked when Chu army appeared in Yiyang battlefield. At that time, Zhang Yi tricked Chu Huaiwang into breaking diplomatic relations with Qi, which led to the fall of Hanzhong and the sharp contradiction in Qin Chu.