势不两立 irreconcilable
Explanation
指敌对的双方不能同时存在，比喻矛盾不可调和。
It means that two opposing sides cannot coexist, and it is a metaphor for irreconcilable contradictions.
Origin Story
话说东汉末年，天下大乱，群雄逐鹿。曹操挟天子以令诸侯，势力日益强大，先后击败袁绍、刘表等诸侯，统一北方指日可待。然而，南方却还有孙权、刘备两大势力，与曹操形成三足鼎立之势。曹操野心勃勃，欲一统天下，于是率大军南下，意欲先灭孙权，再图刘备。孙权得知曹操来势汹汹，召集文武百官商议对策。群臣之中，有主张投降者，也有主张联合刘备抗曹者。最终，孙权采纳了周瑜的建议，与刘备结盟，共同抗击曹操。赤壁之战，曹操惨败，从此奠定了三国鼎立的局面。此后，曹操、孙权、刘备之间，虽然不时有联盟，却也始终矛盾重重，互相对抗，直至魏蜀吴三家各自称帝，形成了你死我活，势不两立的局面。
In the late Eastern Han Dynasty, the country was in chaos, and many heroes were vying for the supremacy. Cao Cao used the emperor to command the feudal lords, and his power grew stronger and stronger. He defeated feudal lords such as Yuan Shao and Liu Biao one after another, and the unification of the north was imminent. However, there were still two major forces in the south, Sun Quan and Liu Bei, forming a three-legged balance with Cao Cao. Cao Cao, with great ambition, wanted to unify the whole country. Therefore, he led his troops south, intending to destroy Sun Quan first and then Liu Bei. Sun Quan, learning that Cao Cao's troops were coming aggressively, summoned his civil and military officials to discuss countermeasures. Among the ministers, some advocated surrender, while others advocated joining forces with Liu Bei to resist Cao Cao. In the end, Sun Quan adopted Zhou Yu's suggestion, formed an alliance with Liu Bei, and jointly resisted Cao Cao. In the Battle of Chibi, Cao Cao was defeated, which laid the foundation for the three kingdoms to stand together. Afterwards, although there were occasional alliances among Cao Cao, Sun Quan and Liu Bei, there were always serious contradictions and mutual conflicts, until Wei, Shu and Wu each proclaimed themselves emperors, forming a life-and-death, irreconcilable situation.
Usage
形容敌对双方矛盾尖锐，不可调和。多用于政治、军事等方面。
To describe the sharp and irreconcilable contradictions between opposing sides. It is often used in political and military contexts.
Examples
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曹操与刘备、孙权势不两立，最终三国鼎立。
Cao Cao yu Liu Bei, Sun Quan shi bu liang li, zhongjiu Sanguo dingli.Zhengyi yu xie'e shi bu liang li, zhongjiu zhengyi bi jiang shengli xie'e
Cao Cao, Liu Bei, and Sun Quan were irreconcilable, and eventually the three kingdoms stood together.
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正义与邪恶势不两立，最终正义必将战胜邪恶。
Justice and evil are irreconcilable, and ultimately justice will prevail.