What is the "sadness of classical frontier poems" in Liangzhou Ci?

"Why do Qiangdi blame the willow? The spring breeze is just Yumen Pass. "

Wang Zhihuan wrote this poem about the homesickness of frontier soldiers. It was written in a desolate and generous way, sad without losing strength. Although it tried to exaggerate the resentment that the garrison soldiers were not allowed to go home, they found nothing.

There is no feeling of depression, which fully shows the broad-minded mind of the poets in the prosperous Tang Dynasty. The first sentence, "The Yellow River is far above the white clouds", captures the characteristics of overlooking and depicts a moving picture: on the vast plateau, the Yellow River runs down and looks at the west as if it were flowing out of the white clouds. The second sentence, "An isolated city, Wan Ren Mountain", is about an isolated city in the fortress. A lonely city located in the frontier fortress, standing tall by mountains and waters. These two sentences describe the majestic momentum of the motherland's mountains and rivers, outline the geographical situation of this important national defense town, highlight the desolate situation of foot soldiers guarding the border, and provide a typical environment for the latter two sentences to describe the psychology of defending the army.

In this environment, I suddenly heard the sound of Qiangdi, and the tune I played happened to be "Folding Willow", which aroused the sadness of the garrison. The ancients had the custom of parting and giving gifts. "Liu" and "Liu" are homophonic and presented to Liu as a souvenir. In the Northern Dynasty Yuefu's "Blowing the Drum Horn Across", there is "Folding Yang Liuzhi", and the lyrics say: "If you don't catch the whip when you get on the horse, you will hit Yang Liuzhi instead. Dismount and play the flute, worrying about killing travelers. " It is mentioned in the song that pedestrians break willows when they walk. This kind of farewell wind was very popular in the Tang Dynasty. Thus, there is a close relationship between willow and parting. Nowadays, when the foot soldiers guarding the border pass hear the sad tune of "Folding Willow" played by Qiangdi, it is inevitable that they will feel sad and not hate it. Therefore, the poet explained in an open-minded tone: Why does Qiangdi always play the sad tune of "breaking willow"? You know, outside Yumenguan is a place where the spring breeze can't blow, and no willow can be folded!