**The effectiveness of ancient strategic decision-making, especially the military deployment during the Three Kingdoms period, is a striking example. In particular, Shu Han's strategic choice of Hanzhong revealed its leadership's deep understanding of the situation and military layout. Here, we focus on Wei Yan and Jiang Wei's Hanzhong defense strategy, and how the military opinions of the two generals affected the fate of Shu Han. Wei Yan's insistence on the "policy of focusing on the door" and Jiang Wei's strategy of "gathering troops and gathering valleys" present a sharp contrast, which intuitively reflects the successes and failures of different military ideas in practice.
Entering the Three Kingdoms period, Hanzhong became the focus of contention between Shu Han and Cao Wei, and strategic deployment became the key to the survival of Shu Han. Wei Yan, as a seasoned general, is well versed in the advantages of geography and the way to stick to it, and put forward the "important policy". This strategy is based on the natural hazards of Hanzhong, using natural mountains as a barrier to build a line of defense. This approach was indeed a prudent defensive strategy for the Shu Han during Liu Bei's period and when he was just succeeded. Wei Yan's layout kept Hanzhong safe and achieved a strong stand in the face of foreign enemies. However, while consolidating national defense, this strategy inevitably consumes a large amount of military and human resources, which may lead to the depletion of national strength in the long run. Wei Yan's layout reflected his accurate grasp of the situation at that time and his superb skills in defensive warfare, but he was slightly lacking in enterprising spirit and failed to give Shu Han more room for development.
On the other hand, Jiang Wei, the background of his takeover of the military power of Shu Han was that the national strength was overdrawn, the people were struggling to make a living, and they urgently needed strategic adjustment. He adopted a more flexible tactic, and "gathering troops in the valley" was theoretically a typical strategy of luring the enemy into deep and then encircling and annihilating the enemy, and this point had its own cleverness at the tactical level. It reflects Jiang Wei's keen perception of the battle situation and the full use of limited resources. However, the implementation of this strategy requires extremely high requirements for the quality of the army and the capabilities of the commanders, and the slightest carelessness can lead to the collapse of the overall situation. Just as his later Northern Expedition failed many times, but accelerated the demise of Shu Han, it can be seen that although its strategy was good, it was difficult to support it under the national strength and situation at that time.
When comparing Wei Yan's "strategy of refocusing on the door" and Jiang Wei's "gathering troops and gathering valleys", we examine not only the success or failure of the two different strategies, but also the different understandings of the two generals on the control of the situation and the use of resources. Wei Yan's strategy seemed too conservative at the time, but it maintained the stability of Hanzhong and the lifeline of Shu Han. Although Jiang Wei's decision-making was forward-looking, due to the changes in the current situation and the scarcity of resources, he ultimately failed to achieve the expected results. The comparison of these two strategies is actually a collision between pragmatism and idealism in the military field, and it also reflects the far-reaching influence of the background of the times and the state of national strength on strategic choices.
Looking at the different defensive strategies of Wei Yan and Jiang Wei against Hanzhong, the conclusions we draw are quite instructive. Although Wei Yan's "heavy policy" was conservative, it was actually in line with the national strength of Shu Han at that time, and maintained Jiang Wei's "gathering troops and gathering valleys" Although it was innovative, it showed its vulnerability at a critical moment due to the high strategic risk. From a historical point of view, the contrast between the two is not only a high level of military level, but also a reflection on the adaptability and sustainability of different strategies. In making realistic military decisions, it is necessary not only to hold firm a solid line of defense, but also to have the flexibility to adapt to changes in a flexible manner, and, still more, to have a profound grasp of the overall situation of the country. For researchers of modern historiography, this historical event provides an example of in-depth analysis of strategic thinking, and also gives us important thinking on how to find a balance between development and development.