A better translation (subjectivly better, it sounds better and is more accurate word for word) is:
"If you wish for peace
, prepare for war
It more or less implies that war is the natural state of humanity
and peace can only be imposed by force. A neat metaphor
for modern american foreign policy
Another tidbit: If you have ever heard of pistol ammunition called 9mm
parabellum, it means just that: 9mm prepare for war.