Si vis pacem, para bellum is a Latin adage translated as, "If you wish for peace, prepare for war" (usually interpreted as meaning peace through strength - a strong society being arguably less likely to be attacked by enemies).
The source of this adage remains unknown; however, it is universally believed, rightly or wrongly, to be based on a quotation from Roman military writer Publius Flavius Vegetius Renatus: Igitur qui desiderat pacem, praeparet bellum. The saying is one of many from or based on his work, Epitoma rei militaris, possibly written around the year 390 AD. It is embedded in a passage that stresses the importance of skillful preparation of military actions (an 'Art of War', so to say) as opposed to mere reliance on coincidence or superiority of numbers:
"Therefore, he who wishes peace, should prepare war; he who desires victory, should carefully train his soldiers; he who wants favorable results, should fight relying on skill, not on chance.
Whatever the source, the adage has become a living vocabulary item itself, used in the production of different ideas in a number of languages. The actual words of Vegetius are not even recognized by a large number of writers, who attribute the saying directly to him.
Si vis bellum para pacem
For example, with reference to the foreign policy of Napoleon Bonaparte, the historian, de Bourrienne, said
"Everyone knows the adage .... Had Bonaparte been a Latin scholar he would probably have reversed it and said, Si vis bellum para pacem."
meaning that if you are planning a war you should put other nations off guard by cultivating peace. Conversely, another interpretation could be that preparing for peace may lead another party to wage war on you.
Si vis pacem para pactum
The idea of insuring peace by deterring war-like powers through armaments took an ominous turn in the 20th century. Perhaps merely being prepared is not enough. Perhaps it is necessary to wage war to deter war. The National Arbitration and Peace Congress of 1907, presided over by Andrew Carnegie, addressed this issue:
"These vast armaments on land and water are being defended as a means, not to wage war, but to prevent war.... there is a safer way ... it requires only the consent and the good-will of the governments. Today they say .... If you want peace, prepare for war. This Congress says in behalf of the people:Si vis pacem, para pactum, if you want peace, agree to keep the peace.
Si vis pacem fac bellum
"If you want peace, make war". The solution does not cover the case of the nation that does not desire peace. Imperial Germany went to war in 1914 and was castigated by Richard Grelling, a German-Jewish pacifist, in J'Accuse (1915). In 1918 Grelling wrote again, this time as an ex-patriate in Switzerland. Citing the "The world must be safe for democracy." speech of Woodrow Wilson before congress on April 2, 1917, Grelling says:
"... when all other means fail, ... the liberation of the world from military domination can in the extreme case only take place by battle. ... in place of the reprehensible si vis pacem para bellum a similarly sounding principle ... may become a necessity: Si vis pacem, fac bellum.
Si vis pacem para pacem
The great wars of the 19th and 20th centuries were opposed by the philosophy of pacifism, which in the 19th century was associated with early socialism, even though the socialism of the 20th often lacked pacific tendencies, preaching violent revolution instead. The pacifism that opposed the world wars traced a lineage to Barthélemy Prosper Enfantin, an early French socialist and one of the founders of Saint-Simonianism. As early as April 2, 1841, he had said in a letter to General Saint-Cyr Nugues:
"Le fameux dicton ... me semble beaucoup moins vrai, pour le XIXɵ síècle, que Si vis pacem, para pacem."
with reference to Algeria. By way of elucidation Enfantin goes on to say that war could have been avoided if a proper study of Algeria had been made.
The main clause of the adage has been used as a motto by German arms maker Deutsche Waffen und Munitionsfabriken (DWM), and is the source of the term Parabellum as applied to firearms and ammunition (especially the 9mm Parabellum, aka 9mm Luger). The term is an opposed parallel to the English use of "peacemaker" to mean the Colt Single Action Army handgun.