In 960 AD, Zhao Kuangyin, a general of the Later Zhou Dynasty, launched a military coup, seized power, and established the Song Dynasty, becoming known as Emperor Taizu of Song.
During the early Song Dynasty, Emperor Taizu was determined to unify China by conquering the smaller states surrounding his domain. Starting in 962 AD, his armies campaigned relentlessly, defeating the regimes of Nanping, Later Shu, and Southern Han, and tightening a noose around the Southern Tang kingdom along the middle and lower Yangtze River.
Li Yu, known historically as the Last Ruler of the Southern Tang, was a master of music, chess, calligraphy, and painting, and a passionate poet—but utterly clueless about state affairs. Raised in the lavish confines of the palace, he lived in extreme luxury. His wife, Queen Zhou the Elder, was both beautiful and talented, yet Li Yu was unsatisfied, often secretly meeting with her younger sister, Zhou the Younger, indulging in endless song, dance, and pleasure.
Facing the growing threat of the Song Dynasty, Li Yu paid it no mind, adopting a policy of seeking temporary peace. He repeatedly sent vast treasures to the Song court and even voluntarily renounced the Southern Tang's imperial title, reducing his kingdom to a vassal state.
But Emperor Taizu of Song, Zhao Kuangyin, was not deterred from his goal of annexing the Southern Tang. In 974 AD, using Li Yu's refusal to appear at court as his pretext, he ordered General Cao Bin to lead a 100,000-strong army to conquer the Southern Tang.
Li Yu, the last ruler of the Southern Tang, was so hopelessly inept that even as the Song army's massive forces bore down on his kingdom, he remained utterly oblivious. It was only when the Song troops reached his capital, Jinling, that he finally snapped awake and ordered a defense—but it was far too late. The Song army breached the city walls, and Li Yu was taken prisoner.
Emperor Zhao Kuangyin summoned Li Yu before the Mingde Tower and granted him the title "Marquis of Disobeying Orders." From then on, Li Yu lived in Kaifeng as a conquered ruler, enduring shame and humiliation, with only his increasingly haggard consort, the once-beautiful Xiao Zhouhou, by his side. Every time he recalled the past, Li Yu was overwhelmed with endless bitterness and regret.
Soon after, Zhao Kuangyin passed away, and his brother Zhao Kuangyi succeeded him, known historically as Emperor Taizong of Song. Taizong frequently sent spies to monitor Li Yu's every move. On one occasion, he even summoned Li Yu's wife, the Younger Empress Zhou, to the palace alone, only allowing her to return the next day. Witnessing this, Li Yu was deeply traumatized emotionally.
On a night in early spring, Li Yu gazed at the scenery outside his small tower, unable to fall asleep for a long time. He poured out his feelings in a famous poem, "The Beautiful Lady Yu," which includes the lines: "Last night the east wind blew again in my small tower; I cannot bear to look back at my lost kingdom in the moonlight."
When this poem reached Emperor Taizong's ears, he could not tolerate a fallen ruler being so restless, so on July 7, 978 AD, under the guise of celebrating a birthday, he had Li Yu poisoned to death.
Later, people used the idiom "Too Painful to Recall" to express their feelings about great changes in life and circumstances.
Source: *Li Yu*, "The Beautiful Lady Yu"
Meaning of the Idiom: Later, the Chinese idiom "不堪回首" came to describe how great changes in life and circumstances are too painful to recall.