Why did Guan Yu take refuge in Cao Cao?

Guan Yu was captured alive because of defeat and had to surrender to Cao Cao.

In the fifth year of Jian 'an, Cao Cao sent Liu Dai and Zhong Wang to attack Liu Bei and was defeated by Liu Bei. Cao Cao went to dispatch troops personally, Liu Bei was defeated and fled to Yuan Shao, and Guan Yu was captured alive and had to surrender. Cao Cao received a gift and was appointed as a partial general.

Later, Yuan Shaopa sent generals Yan Liang, Chunyu Qiong, Guo Tu and others to attack Ada, the satrap of Dongjun, in Baima. Xun You put forward the operational strategy of introducing from the east to the west and tapping the white horse. Cao Cao accepted Xun You's suggestion and personally led the army to rescue him. Yan Liang was frightened and hurried to fight.

Cao Cao appointed Zhang Liao and Guan Yu as strikers. Guan Yu saw that Yan Liang might cover, rode to kill, stabbed Yan Liang to death among all the troops, drew his sword and beheaded Yan Liang, and then returned. No one can stop General Yuan Jun, the siege of the White Horse was solved, and Guan Yu was appointed as the Tinghou of Hanshou.

Guan Yu's story:

Guan Yu heard that Ma Chao surrendered to Liu Bei. He never knew Ma Chao before, so he wrote to Zhuge Liang and asked who Ma Chao's martial function was compared with. Zhuge Liang knew that Guan Yu was arrogant, so he wrote back and said, "Ma Mengqi is both civil and military, and he is very brave. He is a generation of heroes, belonging to Qing Bu and Peng Yue. He can keep pace with Zhang Yide, but not as handsome as you. "

Guan Yu has a beautiful long beard, so Zhuge Liang called him a beard. Guan Yu was very happy to read Zhuge Liang's reply and handed it to the guest's staff for circulation.