Summarize the emotional tone of Chen's A Story of Climbing Yueyang Tower in one sentence, and tell me why?

The whole poem revolves around the word "sadness". The first sentence of the first couplet "East River and West Water of Dongting Lake" was born, which directly pointed out the geographical location of Yueyang Tower from a big point: in the east of Dongting Lake filled with smoke and in the west of the mighty Yangtze River. I can't help but think of Fan Zhongyan's "Yueyang Tower", which says that "the mountains are far away, swallowing the Yangtze River and and heaven remains our neighbourhood". Seeing this extraordinary statement is fascinating, but the second sentence is no longer a vast and boundless scenery, but depicts a peaceful picture, "The curtain is still, the sunset is late", and I look up and see the boundless twilight. The sadness of the scenery sets off the sadness of people. This sentence is also based on the scene. Couplets have changed from the calm scenery description above to strong lyricism. "Landing in Wu and Shu equally" not only refers to the geographical location of landing, but also is a review of history. The history of Wu and Shu competing for Jingzhou seems to reappear again. The two armies of Wu and Shu fought each other, killing each other, with corpses everywhere, rivers of blood, buzzing voices, hooves and weapons ... The distance of history, the bloody battlefield, seems to have appeared again. War, war, what has war brought to people? With such a mood, "when I lean against the lake and the mountain for dusk", the poet is unwilling to appreciate the lakes and mountains, and is full of melancholy and worries, wandering alone. But in the dusk of lakes and mountains, the wandering figure is elongated, just like the author can't figure it out, cutting off the constant sadness and adding a sense of disappointment and loneliness. Recall history, think about the past, feel the times, and feel sad. "Wan Li's visit is still far away, which is more difficult than three years." The poet uttered a cry of pain. Why does he remember the Battle of Wu and Shu? This is because the poet suffered from war after the change of Li Jingkang: Wan Li fled, went south, drifted and was displaced. This is where the poet is sad. Wan Li and Three Years respectively describe their sufferings from the span of time and space, which makes people deeply moved. Climbing high and seeing far can not only ease the sadness in my heart, but also add a little sadness. This endless melancholy is more like a river rolling out when looking far and leaning against danger. Such as Li Yu's "Don't lean on the bar alone, it's infinite, it's hard to see easily", such as Cui Hao's "Only I look at my home, and the twilight fades? It is human nature to have a sad mist on the river waves. What's more, what about a poet who suffers from the pain of an infinite home and country? The pain of national destruction has already penetrated into the bone marrow. This sentence pushed the poet's sadness, injury, sadness and pain to the extreme. The couplets of "the old head hangs over the old wind and frost, and the old wood is infinitely sad" seem to be the poet's self-pity muttering to himself. He lost his mind before he was old. He was anxious and sad for the country, his family, himself and those fellow villagers who lost their homes like himself. When he is obsessed with the past, he will feel hurt. In autumn and frost, he feels that the times are as cold as wind and frost. Don't old dead trees and desolate lakes look like themselves? The endless desolation of being demoted to the end of the world and the infinite sorrow of the country's destruction and death are self-evident.