Belligerents
Background
When Dong Zhuo enthroned Emperor Xian and ruled by terror, the eastern lords formed a punitive coalition under Yuan Shao in 190. The cause was grand; the lords, each hoarding his own strength, dithered before the passes to Luoyang. The only ones who actually drew swords were Sun Jian and Cao Cao.
Course
Sun Jian broke Dong Zhuo’s army head-on at Yangren, taking the head of the commandant Hua Xiong — the coalition’s only clear victory. Cao Cao, pursuing alone, was routed at Xingyang and barely escaped. Under pressure, Dong Zhuo torched Luoyang and dragged the Emperor west to Chang’an; Sun Jian was first into the ruined capital. The coalition then dissolved in its own quarrels.
Outcome & impact
The coalition failed to topple Dong Zhuo, but it cracked his aura of invincibility — and its collapse launched the true age of every-lord-for-himself. It also announced Sun Jian’s prowess and Cao Cao’s resolve to the realm.
History vs. the novelHistoryvsNovel
Both "Guan Yu beheads Hua Xiong while the wine is warm" and the three brothers’ duel with Lü Bu are the novel’s inventions: history gives Hua Xiong to Sun Jian, and no record puts Liu Bei’s band at Hulao. Even the two "gates" were in reality one pass — no battle carries more novelistic paint than this one.