一衣带水 — “A belt-like strip of water”

The idiom 'Yī Yī Dài Shuǐ' originates from 'The History of the Southern Dynasties: Chronicle of Emperor Houzhu of Chen.' The story goes that Emperor Yang Jian of the Sui Dynasty, who replaced the Northern Zhou Dynasty, aspired to unify China. He implemented a series of policies in the north to enrich the country and strengthen its military, leading to a significant increase in national power. In contrast, Chen Shubao, the last emperor of the Chen Dynasty on the south bank of the Yangtze River, was extremely dissolute and neglected state affairs. Although he knew of Emperor Wen's intention to conquer Chen, he relied on the natural barrier of the Yangtze River and did not take the threat seriously.

Once, Emperor Wen of Sui asked his chief minister Gao Ying for a strategy to conquer Chen. Gao Ying replied, 'The crops in Jiangnan (south of the Yangtze) mature earlier than those in Jiangbei (north of the Yangtze). We can announce our intention to attack during their harvest season, which will force them to abandon their farming and deploy troops for defense. After they are prepared, we will withdraw our forces. If we repeat this several times, they will cease to believe our threats. Then, when they are unprepared, we will suddenly launch a real invasion across the river, catching them off guard. Additionally, the grain in Jiangnan is not stored in underground cellars like ours in the north, but in warehouses built with thatch and bamboo. We can secretly send people to set them on fire. If we burn their granaries for several years in a row, the Chen Dynasty's financial strength will be greatly weakened, making it much easier to conquer.'

Emperor Wen of Sui adopted Gao Ying's strategy. After seven years of preparation, in the winter of 588 AD, he ordered the invasion of Chen. Before departing, he said to Gao Ying, 'I am the father and mother of all people under heaven. How can I fail to rescue the common folk there simply because they are separated by a narrow Yangtze River, no wider than a sash?' Emperor Wen was determined to succeed. He appointed Prince Yang Guang as the marshal, leading an army of 500,000 to cross the river southward, launching a fierce attack on Jiankang, the capital of the Chen Dynasty. They swiftly captured Jiankang, took Emperor Houzhu of Chen prisoner, and brought an end to the Chen Dynasty.