Saber Rattling is a term which refers to a rather belligerent style of behavior, generally in politics, which emphasizes show of force, conviction, and general bombastic thrashing.
The main tenet of the Saber Rattling school of thought is that one must never appear weak or indecisive, for opponents look for just that sort of behavior as a sign that the time is right to attack. This weird logic holds that the way to maintain peace is to always seem ready to go to war, never turn down a confrontation. Present a strong facade, and your enemy will invariably back down, and if he doesn't, it furnishes the opportunity to attack him before he gets stronger.
The term has a distinct 19th century European connotation to it, and why not? In addition to being the age of sabers, it was history's grand expose of this type of mentality. Countless wars were nearly fought during the 19th century as a result of this kind of statesmanship, between every conceivable combination of great powers, and in the end, saber rattling resulted in The Great War.
It is fortunate for us, and we can thank god for it, that saber rattling has gone the way of the saber in our times, alleviating any worry we may have over similar testosterone fueled diplomatic catastrophes.