Because although they have a good relationship since childhood, they all have different goals in life after adulthood, and they all have their own ideals and ambitions. If they form opposites, there must be wars.

In the historical records of all military strategists in China, it can be said that the relationship between Cao Cao and Yuan Shao is very delicate, because they are both young. When I was young, I went to school together, so I was a classmate and the captain of Xiyuan, so I was a comrade-in-arms. No matter what kind of relationship, the relationship between the two is iron and iron.

When they grew up, Cao Cao and Yuan Shao both became officials and military leaders, and their positions on some issues gradually diverged. The first is whether Emperor Xian of Han Dynasty served the public. At that time, it was known that Emperor Xian of Han Dynasty was proclaimed by Dong Zhuo, and many governors recognized Emperor Xian of Han Dynasty before. However, Yuan Shao and Hou Meng of Jizhou wanted to be proclaimed emperor again. Cao Cao had anticipated Yuan Shao's wishful thinking and opposed him.

After that, there were many different opinions on some military strategies, which gradually produced many contradictions. There was another problem, starting from Liu Xie's succession. There was not much confusion in the country, and Dong Zhuo recommended him to ascend to the throne, with Dong Zhuo and Cao Cao assisting him in the dynasties. So Cao Cao took the lead. Cao Cao defeated Yuan Shao in wisdom and strategy. Cao Cao benefited, Yuan Shao saw it in his eyes and was jealous in his heart.

Until the end, their contradictions became more and more prominent. During the battle of Guandu, Cao Cao's team was still short of food and grass. In this case, Cao Cao refused to retreat, and the two princes finally went to war in order to win.