Historically, Guo Jia was very active in Cao Cao's crusade against the north after Cao Cao's victory in Guandu, and he persuaded Cao Cao to withdraw from the army when Cao Cao first hit Yecheng, and attacked Liu Biao first, so that the Yuan clan could fight internally, and finally Cao Cao could take advantage of the situation, and was praised by later generations.

But in fact, this was a major mistake made by Guo Jia in the northern decision-making, which directly slowed down the pace of Cao Cao's unification of the north, one of which prevented Cao Cao from taking advantage of the victory to pursue, and failed to take the opportunity to attack Yecheng, so that Yuan Shang and Yuan Tan escaped, and the second was to suggest that Cao Cao crusade against Liu Biao, dispersing the forces of Cao's army.

【Lost Opportunity】

In Cao Cao's group, Guo Jia is not the first strategist to propose to wait for the enemy's internal fighting and then crusade, as early as when Cao Cao crusaded against Zhang Xiu, Cao Cao's mastermind Xun You had already made a similar suggestion to Cao Cao, when Cao Cao decided to personally crusade against Nanyang, Xun You advised Cao Cao to wait first, and waited until Zhang Xiu and Liu Biao had a conflict in sending troops, but Cao Cao did not listen, Liu Biao and Zhang Xiu were closely united under the pressure of Cao Cao to give Cao Cao a big pain, and then Cao Cao personally expressed his apology to Xun You.

A brief comparison of the two proposals.

Xun You persuaded Cao Cao to postpone sending troops because Cao Cao's strength was unable to forcibly swallow Zhang Xiu, who had Liu Biao's support at that time, and Guo Jia persuaded Cao Cao to stop, thinking that he could wait for Yuan Tan and Yuan Shang to fight inwardly, and then take the opportunity to seize the north.

In terms of time, Xun You said it before Cao Cao officially sent troops, and Guo Jia told Cao Cao to withdraw his troops when Cao Cao had already hit the enemy's base camp Yecheng.

As a result, Cao Cao ended up in Nanyang without success, and apologized to Xun You, proving that Xun You's decision was correct, and after Cao Cao left Yecheng, the Yuan brothers were really as Guo Jia expected civil strife, and Cao Cao also took the opportunity to seize the four northern states, as if Guo Jia was also right, but in fact? Guo Jia is a snake to add.

Because Cao Cao could obviously take Yuan Tan and Yuan Shang in Yecheng at that time, why wait? Yuan Tan and Yuan Shang had been defeated by Cao Cao in the previous battle, and now they can only trap Yecheng, and Cao Cao is likely to defeat Yecheng directly as long as he takes advantage of the victory to pursue, and Cao Cao has this strength at that time.

Guo Jia persuaded Cao Cao that Yuan Tan and Yuan Shang's brothers were not in harmony, and they could suspend the offensive and wait for them to fight inwardly, which did seem reasonable, but it was precisely the reason why Cao Cao had to attack Yecheng! Yuan Tan and Yuan Shang didn't fight when they were together, when would they fight?

The two brothers are not of the same mind, that is to say, Yecheng has two masters, they are wary of each other, vigilant against each other, and distrust each other, at this time Yecheng's defense has dropped to a low point, and the pressure given to them by Cao Cao will only make the rift between Yuan Tan and Yuan Shang expand, and eventually there will be variables, but it will not make them together,

Yuan Tan and Yuan Shang are preparing to annex each other, Yuan Shang is unable to hope that Yuan Tan will become bigger because he has taken his brother's position, so as to threaten himself, and Yuan Tan wants to regain his rightful position, so he wants to replace him, their contradictions are irreconcilable, not to mention that there may be Guo Tu and others to sow discord.

This is completely different from the previous situation of Zhang Xiu and Liu Biao, Zhang Xiu wants to keep his Nanyang, Liu Biao does not want his door to be lost, so they can only be more united under external pressure, they can withstand the pressure, but the Yuan brothers will only collapse under pressure.

Both of them were much easier to deal with in Yecheng than one person in Yecheng, and later when Cao Cao crusaded against Ma Chao and other Xiliang rebels, Han Sui's reinforcements did not accelerate Cao Cao's victory.

At that time, if Cao Cao concentrated his forces on fighting Yecheng to the death, it was very likely that he would break through Yecheng in the eighth year of Jian'an (203), and wipe out Yuan Tan and Yuan Shang, so as to get Jizhou and Qingzhou, and Yuan Xi could not hold Youzhou at all, Cao Cao had not sent troops to Youzhou in history, and the senior cadres of the state were also very likely to see Cao Cao's great strength and surrender directly, that is, in the eighth year of Jian'an, Cao Cao originally had the opportunity to decide the four northern states in a war, and it was quite likely to succeed at one time, but in the end, Cao Cao gave up at Guo Jia's suggestion, After that, more time and effort had to be spent to seize the north.

After Yuan Tan and Yuan Shang fought inwardly, Cao Cao attacked twice, and the second time it took more than half a year to conquer Yecheng, which was guarded by the judge, and then it was a crusade against Yuan Tan, and an attack on Gao Gan, and Yuan Shang and Yuan Xi were missed, and they had to send troops to Wuheng from afar, which may not have been needed.

【North-South Decision】

After the victory of Guandu, the Cao Cao group, led by Xun Yu and Xun You, advocated putting Liu Biao aside, first crusading against the north and eliminating the Yuan group, while Guo Jia and others hoped to condone the civil strife between the two Yuan and first crusade against Liu Biao in the south. And Cao Cao himself was more inclined to crusade against Liu Biao first, and had already had the idea of marching into Jingzhou before Yuan Shao died, but was advised by Xun Yu to make a northern expedition to Yuan.

At that time, Xun Yu's point of view was relatively clear, he thought that he should destroy the northern enemy before Yuan Shao died, and did not give them a chance to breathe, and the crusade against Liu Biao would only give Yuan Shao a chance to turn over, and then Cao Cao listened to Xun Yu's advice, and went north to achieve rich results, and directly hit Yecheng, the base camp of the old Yuan family, but was dissuaded by Guo Jia to retreat.

At that time, Guo Jia not only prevented Cao Cao's further offensive, but also advised Cao Cao to take the opportunity to crusade against Liu Biao, and Guo Jia was also the only strategist who recorded advising Cao Cao to go south before Cao Cao pacified the north. In the reminiscences of Cao Cao in "Fu Zi", there is also a clear record of "However, with the common discussion, the cloud should be the first to determine Jing".

At that time, Guo Jia persuaded many people, and with Cao Cao's support, he almost made the trip south. However, later there was internal turmoil in the Yuan clan, and Yuan Tan, in order to fight against Yuan Shang, sent Xin Bi as an envoy to Cao Cao for help at the suggestion of Guo Tu.

At this time, Xun You, as Cao Cao's mastermind, dissuaded Cao Cao, and then Xin Bi made up his mind when Cao Cao hesitated, and Cao Cao led his army north.

During this period of time, Guo Jia's support for the Southern Expedition to Liu Biao was relatively clear, he not only mentioned it directly, but later when Xin Bi looked for Guo Jia, he could also see Guo Jia's attitude. But judging from the situation at the time, it was not a good strategy to attack Liu Biao first.

Liu Biao was more conservative in history, the attack was insufficient, and the threat to Cao Cao was not great, but it was not easy to fight, which can be seen from Cao Cao's attack on Nanyang back then. And Yuan was the strongest prince outside of Cao Cao at that time, if Yuan Shang took advantage of Cao Cao's crusade against Liu Biao to eliminate Yuan Tan and remove internal troubles, then it would not be so easy for Cao Cao to seize the north, and Yuan Shang would attack from Cao Cao's rear when Cao Cao was dealing with Liu Biao, which would be even worse for Cao Cao.

On the contrary, at that time, Yuan Tan's submission to Cao Cao would not be an obstacle to Cao Cao's march to the north for the time being, and Cao Cao had to face only Yuan Shang, and Cao Cao could take advantage of Yuan Shang's crusade against Yuan Tan to march again, and the probability of success was very high, so Cao Cao finally gave up going south and turned north.

And Guo Jia is also a smart person, knowing that if he chooses, so he never had any other objections to Beishang later.