Under what background was Li Bai's "I heard that Wang Changling was going to move the Dragon Label" written?

This poem was written in the eighth year of Emperor Xuanzong of Tang Dynasty (749) and the twelfth year of Emperor Xuanzong of Tang Dynasty (753). In short, it was made by Li Bai at the age of 50. At that time, Wang Changling was demoted from Jiangningcheng to Longbiao County (now Qianyang County, Huaihua, Hunan Province), and Li Bai wrote this poem after hearing that his friend was demoted to Yangzhou.

"I heard that Wang Changling moved to Longbiao kiln, and this is from him"-Li Bai (Tang)

After the easy autumn, cuckoo clock, I heard you pass five streams.

I entrust my sad thoughts to the moon, hoping to accompany you to the west of Yelang.

After Huayang finished singing, I heard that you were demoted to captain of Longbiao, and that remote place of Longbiao had to pass through Wuxi. I put my sad thoughts on the bright moon, hoping it can accompany you to Yelangxi with the wind.

Extended data

"Huayang has landed, and Wendaolong has passed the five streams." From the beginning, I chose two things with local characteristics, Huayang (catkin) and Zigui (cuckoo), to describe the late spring scene in the south and set off a sad atmosphere.

Wang Changling was demoted as a barren land in the Tang Dynasty. The first two sentences seem dull, but they actually contain rich contents, which have many functions: they write down the time, the atmosphere, point out the topic and pave the way for the next two sentences.

"I am worried about the bright moon, and I will go to Yelangxi with the wind." Because Li Bai was in Yangzhou at that time, there was no way to bid farewell to Wang Changling personally, so he had to entrust a piece of affection to Mingyue. What is well written here is a common sense. People walk at night. "The moon has gone, so have I." The moon always walks with us silently.

Li Bai turned Yue Ming into his body double and accompanied his unfortunate friend to the west of Yelang County. (This intention was also used once by Li Bai in Mount Emei on a Moonlit Night. )

Li Bai's poems and songs are always full of romanticism, and the distance between time and space is not his obstacle. With the intention of the bright moon, the friendship between friends is profound and subtle at once.