漢獻帝建安四年時，對曹操威脅最大的，是據守在北方的袁紹。隔年，兩軍正式交戰在陽武（今河南省陽武縣），曹操的兵力遠不如袁紹的十萬大軍，加上曹軍的軍糧所剩不多，士兵又累，曹操陷入苦戰，這時，袁紹的謀士許攸卻跑來投奔曹操。曹操便詢問許攸如何對付袁紹，許攸建議用智取，不要正面攻擊，並且告知袁紹的軍糧都放在烏巢（河南省延津縣東南），那裡沒有很多兵力看守，建議突襲糧倉放火燒糧，讓十萬大軍斷糧，這樣就可以削減袁紹的軍力。果然，當袁紹知道糧草失火消息，便派部分軍隊前往營救，結果還是搶救失敗。另外，主力軍攻向曹軍所在處官渡也戰敗，全軍士氣瓦解，士兵逃的逃，死的死，十萬大軍只剩兩萬左右，袁紹的政權就瓦解了。
三十六計之第十九計：釜底抽薪
原指要停止沸騰的水，直接抽走鍋底下的柴木，也就是解決問題要從根本上著手。此指不直接與敵軍正面衝突，改用其它辦法將敵軍的實力及氣勢削減。
In the fourth year of Han emperor Sian's Jian An period, the biggest threat to Cao Cao was Yuan Shao who was entrenched in the north.
The next year, the two armies formally engaged in battle at Yang Wu. The strength of Cao Cao's forces numbered far less than Yuan Shao's army of one hundred thousand. Furthermore, Cao Cao's food supply was running low, and his soldiers were exhausted. It was a really bad situation for Cao Cao. However, at this time, Syu You, the advisor to Yuan Shao, unexpectedly chose to defect to the side of Cao Cao.
Cao Cao asked Syu You for ideas on how to fight Yuan Shao. Syu You suggested that instead of a frontal attack against Yuan Shao's larger force, it is better to use win by wit. He informed Cao Cao that the food supply for the Yuan army was stored at a placed called Wu Chao, and its defense was minimal. Syu You suggested a raid to burn down the barns where all the food was stored. A sudden cut in food supply for all one hundred thousand soldiers would surely reduce the strength of the Yuan army.
Indeed, when Yuan Shao heard the news of the fire, he sent some of his troops to rescue the food supply. Of course, their efforts were in vain. Apart from that, Yuan Shao's main force which headed for Guan Du, where the Cao army was encamped, was defeated as well. Without food, the morale of his troops soon collapsed. The soldiers either fled or were killed. As a result, Yuan Shao's army of one hundred thousand strong was reduced to a mere twenty thousand. As a consequence, Yuan Shao's regime collapsed.
Strategy 19: Removing the Firewood From Under the Stove
The best way to stop the water from boiling is to remove the firewood from the stove. In other words, you've got to solve a problem by tackling its source. Here it means you don't have to defeat an enemy by defeating it on the battlefield. Instead, you can use other means to weaken the strength and the morale of the enemy.
