In the late Eastern Han Dynasty, eunuchs monopolized power. Officials heavily extorted the people's wealth, and the overburdened populace finally erupted in the Yellow Turban peasant uprising in the spring of 184 AD.
The Yellow Turban Rebellion swept across the land with overwhelming force, and peasants everywhere rose in response. In Fuhan, a farmer named Song Jian also rebelled, allying with the Qiang and Hu peoples to seize Jincheng Commandery. They elected the local strongman Han Sui as their leader, and though the imperial court sent troops several times, each campaign ended in failure. Seeing other regional warlords carving up territories for themselves, Song Jian established his own small kingdom.
In 196 AD, Cao Cao "held the emperor hostage to command the nobles," using Emperor Xian of Han's name to campaign east and west, unifying northern China.
Cao Cao, determined to unify the realm, led a western campaign in 211 AD, crushing the 100,000-strong allied forces of Han Sui and Ma Chao. After seizing Chang'an, he ordered his trusted general Xiahou Yuan to hold the city.
After three years of relentless campaigning, Xiahou Yuan drove Ma Chao into retreat and cornered Han Sui at Luoyang. With Song Jian's reinforcements, Han Sui prepared to hold the city at all costs. But Xiahou Yuan set fire to the Qiang villages, luring Han Sui out to save them. At the Battle of Changli, Han Sui's entire army was annihilated.
Xiahou Yuan pressed his advantage, and his vanguard Zhang He soon laid siege to Fuhan, where both sides reached a stalemate. Leading his main army in a fierce assault, Xiahou Yuan finally captured the city after over a month of relentless attacks. Song Jian, refusing to surrender even unto death, was executed on the spot.
Upon receiving the battle report, Cao Cao was overjoyed and praised Xiahou Yuan, saying, "Song Jian has been in rebellion for over 30 years, and today you have crushed him in one stroke. General, you truly 'stride like a tiger west of the pass, unstoppable and unmatched.'" Later, people used the idiom "unstoppable and unmatched" to describe an invincible military force.
Source: *Records of the Three Kingdoms*, "Book of Wei: Biography of Xiahou Yuan"
Meaning of the Idiom: Later, the Chinese idiom "所向无前" came to describe an invincible military force.