I believe that many people who have watched the Three Kingdoms are aggrieved that the Shu Han failed to unify the world in the end, and the Han family was just lost. But in fact, there are many reasons why it failed to unify the world. Putting aside the other hardware of the Shu Han (geographic location, food, soldiers, etc.), the lack of generals is actually a flaw.

Zhuge Liang
At this point, you may say that if Liu Xuande hadn't attacked Wu in a rage, resulting in the loss of all the best soldiers and generals, this would not have happened. Although Xuande was wrong, there was one person who was also wrong, and that was Zhuge Liang. He shouldn't have killed the two generals. If they had survived, they would not only have made great achievements in the later Northern Expedition, but they might even have achieved great things. So who are these two people? Let me tell you in detail below.
Liu Feng
He was originally the son of Luohou Kou. Later Liu Bei came to Jingzhou and adopted him as his adopted son. Liu Feng later made many military exploits in Liu Bei's battle to enter Shu. He conquered all the places he fought. After occupying Shangyong, he was named deputy general. However, Zhuge Liang persuaded Liu Bei to kill such a good general.

Liu Feng
Why? First of all, Liu Feng's own problems, first: not saving Guan Yu, which resulted in a generation of heroes losing their heads. Second: He bullied Mengda and forced others to rebel, causing the loss of the three counties in the east. Secondly, this is also a very important reason. He has great achievements and holds great power. If he is retained, he will be a big threat to Liu Chan 's accession to the throne. So to sum up, Liu Feng was executed in the end.
Although I admit that he deserved his death, he would still be a good general if he could stay. Although Liu Feng is arrogant and unkind, he is after all a good general who can rival Cao Zhen in the future. There is no need to kill him when he loses his land and returns to Chengdu. It is a good idea to lock him up and kill him first, and then comfort him with good words to make him guilty and perform meritorious service. After all, Liu Feng has been with Liu Bei for so long, and if he thinks about his old relationship, he will most likely realize his mistakes and change his ways to kill the enemy bravely and make meritorious deeds. As for worrying about whether Liu Chan's throne can be secure, let alone worry about it. With Li Yan Zhuge Liang can't make any big waves in Liu Feng.
If Liu Feng is still alive, it will undoubtedly alleviate the Shu Han situation of "there are no generals in Shu, Liao Hua is the pioneer". After all, "Three Kingdoms" said that when he attacked Yizhou, he "conquered everything". Putting this kind of record into the Northern Expedition, it is estimated that the difficulty of conquering cities and territories will be greatly reduced. Therefore, Zhuge Liang should not kill Liu Feng, but should give him a chance to make meritorious service and add a sweet date to make him work honestly.
Ma Su
Ma Su and his brother Ma Liang followed Liu Bei together in their early years and served as prefects, county magistrates and other officials in various places. Not only that, he also read poetry and books, knew the art of war, and once made suggestions for Zhuge Liang. He made great achievements in pacifying Yong Kai and subduing Meng Huo Ma Di. But the fly in the ointment is that he can only talk on paper and lacks actual combat experience. During the first Northern Expedition, because of his arrogance and disobedience, the most likely success of the Northern Expedition fell short. As a result, Zhuge Liang had to kill him to correct military law. Liu Bei also said before he died that Ma Di was a man who talked on paper and liked to talk big words, but had no practical talents. Such a person should not be entrusted with important responsibilities.

Ma Su
Although Ma Su is indeed unfit for reuse, we cannot beat him to death with a stick. In Ma Su's case, according to current terms, he is a master of theory but a novice in practice. Zhuge Liang could actually let Ma Di perform meritorious service and spare his life. After all, Ma Di was a good helper. Why did Zhuge Liang die of illness in the end Wuzhangyuan ? It was because he did everything by himself, which led to him being exhausted to death. If Ma Su is still alive, he can definitely help him share the work and let Zhuge Liang rest. The fifth Northern Expedition may be successful.
Ma Su may not be capable now, but following Zhuge Liang's Northern Expedition and his experience in brushing, he may gradually grow, and he may even be able to stand alone in the future. Battle of Wuzhangyuan If Ma Su was here, maybe Zhuge Liang could spend as much time as he wanted with the Wei army and find suitable fighters to break through, and he wouldn't be so tired. After all, there were three rebellions in Huainan later, and Zhuge Liang might seize this opportunity to make a comeback. You might say that Ma Su performed poorly the first time, and using him later would make the Northern Expedition even worse.I don't think so. Ma Su will probably learn from his first loss and get back on his feet. It's a pity that the military law at that time was difficult to tolerate, and Zhuge Liang was not ruthless enough to protect Ma Su, otherwise what would happen next was unknown.

Zhuge Liang
To sum up, I think Zhuge Liang's killing of Liu Feng and Ma Di was a failure. Although their crimes are not punishable, at the moment Shu Han is employing people, staying here can also add security for Shu Han to seize the world. Although history is in the past, judging from the contributions of Ma Su and Liu Feng, they are indispensable talents. They don't need to be executed. They can be severely punished and can be induced to realize their mistakes and correct them. Then give them a chance to make meritorious service, and maybe they will shine in the subsequent Northern Expedition.
With Liu Feng here, we will not be afraid of unscrupulous generals leading troops to fight. With Ma Su around, Zhuge Liang would not be so tired in the later period. Someone could share the pressure and he could continue to spend time with Sima Yi without having to do everything. Therefore, the two generals Zhuge Liang should not kill are Ma Di and Liu Feng. If they were alive, Zhuge Liang's Northern Expedition would be much smoother. Moreover, it is very possible to conquer the Central Plains in the north and restore the Han Dynasty.