As the first sentence of a poem, "The emperor of China yearns for the beauty that may shake an empire", what role does it play in structure and content?

The first sentence at the beginning of the poem: "The emperor of China longs for beautiful women who may shake an empire" seems very common, as if the story should be written from here without the attention of the author. In fact, these seven words are extremely rich, which is the whole program, which not only reveals the tragic factors of the story, but also evokes and directs the whole poem. Then, in extremely frugal language, the poet described how Xuanzong of the Tang Dynasty emphasized color and sought color before the Anshi Rebellion, and finally got Yang Guifei, who said, "As long as she turns her head and smiles, there will be a hundred spells, and the makeup of the sixth palace will go up in smoke." It describes the beauty and charm of Yang Guifei. After entering the palace, he was favored by color. She not only "inherited her kindness", but also "listed all her sisters and brothers in the soil". Repeatedly rendering how Tang Xuanzong indulged in debauchery, how to have fun, and how to indulge in singing, dancing and drinking in the palace all day. All this led to the Anshi Rebellion: "Until the drums of war exploded from Yuyang, shaking the earth and breaking the tune of rainbow skirts and feather clothes". This part describes the internal cause of "long hatred", which is the basis of the tragic story. Through the realistic description of this court life, the poet ironically introduced the hero and heroine of the story: an emperor who valued the country and despised the people, and a charming and pampered concubine. This also vividly implies that the misunderstanding of Tang Xuanzong is the root of this tragedy.