How to understand the theme of Bai Juyi's long poem Song of Eternal Sorrow

Song of Eternal Sorrow is a long narrative poem by Bai Juyi, a poet in the Tang Dynasty. The whole poem vividly describes the love tragedy between Xuanzong of Tang Dynasty and Yang Guifei. With the help of historical figures and legends, poets have created touching stories and reproduced the truth of real life through their own artistic images, which have infected readers for thousands of years. The theme of this poem is "Song of Eternal Sorrow".

This poem is one of Bai Juyi's most outstanding works, and it is also one of the models of the close combination of lyric poetry and narrative poetry in China's classical poetry. At the beginning of the poem, both the hero and heroine were condemned, but with its development, the poet enriched the story with his own feelings and imagination, giving this love tragedy a more universal meaning, which made the author and readers have a high degree of sympathy for it. To some extent, it broke away from the true colors of history and became a sentimental "amorous feelings" poem, mainly praising the love between Li and Yang.