In 198 AD, Lü Bu, who was in Xuzhou, betrayed the imperial court and allied with Yuan Shu, when Lü Bu sent troops to attack Liu Bei, who was stationed in Xiaopei, although Cao Cao sent Xiahou Huan to assist Liu Bei, but the generals led by Gao Shun at that time were good at war, Liu Bei and Xiahou Huan were not his opponents, so in September, Gao Shun attacked Xiao Pei, Liu Bei could only flee, so he defected to Cao Cao. In order to compete for Xuzhou, Cao Cao immediately led a large army and attacked Lü Bu with Liu Bei. Because Cao Cao had more troops and was able to fight well, Lü Bu could not defeat Cao Cao, so he planned to ask Yuan Shu for help, but Cao Cao was determined to defeat Lü Bu, so Lü Bu's reinforcements had not yet arrived, and his internal rebellion had already begun. At that time, Wei Xu and others kidnapped Chen Gong and came to surrender to Cao Cao, and Lü Bu, seeing that the general situation was gone, also surrendered to Cao Cao.
However, although Lü Bu surrendered to Cao Cao, he did not think of sacrificing himself to death, for this reason, he did not hesitate to intercede with Cao Cao, he said that he was brave and good at war, as long as Cao Cao was willing to reuse himself, he would be able to unify the world, but at this time Liu Bei reminded Cao Cao that he hoped that Cao Cao could think about the fate of Ding Yuan and Dong Zhuo, and Cao Cao would kill Lü Bu after listening to Liu Bei's words. Some people believe that the reason why Cao Cao wanted to kill Lü Bu instead of reusing him was mainly because Cao Cao had no way to control Lü Bu.
In fact, if from a historical point of view, Cao Cao is not incapable of controlling Lü Bu, And Zhang Xiu Cao Cao, who repeatedly surrendered at Bijiguan, dares to accept it, Lü Bu is naturally not a problem, but in the Romance of the Three Kingdoms, Cao Cao is indeed unable to control Lü Bu. Because in the rendition, Lü Bu is a person without moral and ethical constraints, he just does it, and never reflects on the impact of his doing so, because of this, Cao Cao will surrender today, tomorrow may send troops to occupy your city, just because Lü Bu is too unprincipled, Cao Cao even if he accepts Lü Bu, he can't control it, which will kill the world's first fierce general.
What's more, Lü Bu in the book can set off a monstrous wave as long as he has a little military strength, Cao Cao's Yanzhou was almost conquered by Lü Bu, and Xuzhou occupied by Liu Bei was also attacked by Lü Bu, which shows that Lü Bu will not only rebel, but also because his force value is too strong, so that once he rebels, it is difficult to suppress it, but also because Lü Bu is too strong, Cao Cao is not sure to leave Lü Bu alive, in order not to be from the previous Yanzhou was broken, Cao Cao can only kill Lü Bu.
The author believes that from the perspective of the "Romance of the Three Kingdoms", Lü Bu has no principles in doing things, and his ability is too strong, for Cao Cao, such a person is indeed unable to control himself, so it is also reasonable that Lü Bu, who was captured, was eventually killed.