During the Spring and Autumn Period, Duke Li of Jin, swayed by slander, arbitrarily killed his ministers and brought suffering to the people. In 573 BCE, senior official Luan Shu led a coup, killed Duke Li, and brought Prince Ji Zhou back from abroad to rule, historically known as Duke Dao of Jin. Young and capable, Duke Dao appointed talented individuals, gradually revitalizing the state.
During the Spring and Autumn period, nomadic tribes collectively known as the Rong and Di frequently raided the northern borders of the state of Jin. In 569 BCE, their chieftain sent envoys bearing lavish gifts to the Jin court, seeking an alliance through the minister Wei Jiang.
Duke Dao of Jin was skeptical that the Rong and Di tribes would ever show goodwill, insisting, "Only military force can solve this." Wei Jiang replied, "Many states are now bullied by the great Chu, and they look to Jin for aid. If we ally with the Rong and Di, we can remove worries from our rear and focus all our strength on Chu." The Duke found his reasoning sound and signed a treaty with the tribes.
During the Spring and Autumn period, the small state of Zheng, caught between the powerful states of Jin and Chu, was constantly forced to switch allegiances. Initially loyal to Jin, Zheng was repeatedly attacked by Chu and eventually submitted. When Jin sent troops to help, Zheng turned back to Jin—but the moment Jin's army withdrew, Zheng promptly bowed to Chu once more.
Duke Dao of Jin was furious at Zheng's defiance, so he allied with twelve other states, including Wei and Qi, to launch a joint attack. Duke Jian of Zheng, seeing the massive army at his borders, panicked and sent his prince bearing lavish gifts to the Jin camp to sue for peace. Duke Dao, satisfied that Zheng had submitted, agreed to the truce.
This victory showcased Jin's military might and elevated its prestige, leaving Duke Dao of Jin overjoyed. Remembering Wei Jiang's contributions in pacifying the Rong tribes, the duke decided to share half of the gifts from Zheng with him as a reward.
Wei Jiang declined, saying, "This is entirely due to your majesty's virtue and the contributions of your ministers. I hope that while enjoying pleasure, you will not forget the ancient saying: 'Be vigilant in peace, be prepared against danger.' Only then can you enjoy lasting happiness!"
Later, people used the idiom "Be Vigilant in Peace" to mean staying aware of potential dangers and difficulties even when in a safe and trouble-free environment.
Source: *Zuo Zhuan*, Chapter "Duke Xiang, Eleventh Year"
Meaning of the Idiom: Later, the Chinese idiom "居安思危" came to describe staying aware of potential dangers and difficulties even when in a safe and trouble-free environment.