During the Spring and Autumn period, wars between the feudal states were constant.
In 719 BCE, the states of Chen and Wei allied to attack their neighbor Zheng, whose ruler, Duke Zhuang of Zheng, sought peace by sending a message to Duke Huan of Chen, but Duke Huan refused.
Prince Tuo Wufu, younger brother of Duke Huan of Chen, advised, "To embrace benevolence and foster goodwill with neighboring states should be a nation's fundamental policy. Since Duke Zhuang of Zheng seeks peace, we should accept his request and maintain friendly relations with Zheng."
Chen Huangong refused to listen. He said angrily, "Song and Wei are very powerful. As long as we are friendly with them, why should we fear a tiny state like Zheng!"
Thus, Duke Huan of Chen allied with the state of Wei and dealt Zheng a crushing defeat.
Two years later, in 717 AD, the State of Zheng had grown strong through diligent governance. Seeking revenge, Duke Zhuang of Zheng launched an attack on the State of Chen. Chen suffered a crushing defeat, yet the neighboring states of Song and Wei stood by and offered no assistance.
Later, the historian who compiled *Zuo's Commentary* remarked, "Good must not be lost, and evil must not be allowed to grow—this is a lesson for Duke Huan of Chen. He nurtured evil without repentance and thus brought disaster upon himself. Therefore, when we encounter evil, we must act like a farmer weeding his field: pull it out by the roots and prevent it from regrowing. Only by removing evil can good flourish."
Later, the idiom "cut the weeds and dig up the roots" came to mean eliminating the source of trouble completely, leaving no future problems.
Source: *Zuo Zhuan*, Chapter "The Sixth Year of Duke Yin"
Meaning of the Idiom: Later, the Chinese idiom "斩草除根" came to describe eliminating the source of trouble completely, leaving no future problems.