https://en.wikipedia.org/wiki/Si_vis_pacem%2C_para_bellum

Si vis pacem, para bellum (Classical Latin: [siː wiːs ˈpaːkɛ̃ ˈparaː ˈbɛllʊ̃]) is a Latin adage translated as “If you want peace, prepare for war.” The phrase is adapted from a statement found in Roman author Publius Flavius Vegetius Renatus’s tract Dē Rē Mīlitārī (fourth or fifth century AD), in which the actual phrasing is Igitur quī dēsīderat pācem, præparet bellum (“Therefore let him who desires peace prepare for war”). The idea which it conveys also appears in earlier works such as Plato’s Nomoi (Laws). The phrase presents the insight that the conditions of peace are often preserved by a readiness to make war when necessary.