宿敌

guó jì zhèng zhì zhōng sù dí jī hū kě yǐ zài yī yè jiān jiù chéng wéi méng yǒu

国际政治中，宿敌几乎可以在一夜间就成为盟友。

In international politics, inveterate enemies can become allies almost overnight.

wǒ de jiā zú shì tā jiā zú de sù dí

我的家族是他家族的宿敌。

My family was the arch-enemy of his family.