同室操戈 Internecine strife
Explanation
指内部的人自相残杀，互相争斗。通常形容兄弟之间、亲属之间、或团体内部的激烈斗争。
Refers to the mutual slaughter and fighting of people within a group. Usually used to describe fierce struggles between brothers, relatives, or within a group.
Origin Story
春秋时期，郑国有两位公子，公孙黑和公孙楚。他们同时爱上了同一个女子，引发了激烈的争夺。公孙黑武力强悍，公孙楚文采出众。为了争夺美人，两人最终大打出手，同室操戈，上演了一出令人惋惜的兄弟阋墙的悲剧。最后，郑庄公不得已，只好将这两人分别调离京城，才平息了这场风波。这段历史故事警示着我们，即使是亲兄弟，为了私利而发生冲突，也会造成难以弥补的伤害，更不要说在国家大事面前同室操戈，那是对国家社稷的巨大损伤。
During the Spring and Autumn period in ancient China, two princes, Gongsun Hei and Gongsun Chu, lived in the state of Zheng. They both fell in love with the same woman, leading to a fierce struggle. Gongsun Hei was strong and aggressive, while Gongsun Chu excelled in talent and scholarship. In their fight for the woman, they finally resorted to arms and engaged in a brutal confrontation—an example of internecine strife and internal conflict. Eventually, Duke Zhuang of Zheng had to intervene and remove both princes from the capital to end the conflict.
Usage
多用于比喻内部的冲突和斗争，含贬义。
Mostly used to describe internal conflicts and struggles, with a negative connotation.
Examples
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兄弟俩为了家产闹得不可开交，真是同室操戈，自相残杀。
xiōngdì liǎng wèi le jiāchǎn nào de bùkě kāijiāo, zhēnshi tóngshì cāogē, zìxiāng cánshā.
The two brothers fought fiercely for the family property, it was a real case of internecine strife and mutual slaughter.
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公司内部派系斗争激烈，简直就是同室操戈，令人痛心。
gōngsī nèibù pàixì dòuzhēng jīliè, jiǎnzhí jiùshì tóngshì cāogē, lìng rén tòngxīn
The factional struggles within the company are fierce, it's like a civil war, heartbreaking to watch.