Belligerent, bellicose, pugnacious, combative, quarrelsome, contentious mean having or taking an aggressive or fighting attitude.
Belligerent usually implies actual engagement in hostilities.
When applied to such things as tones, speeches, or gestures, the term implies an actively hostile mood or warlike temper.
Bellicose applies usually to a state of mind or temper; it suggests a desire or readiness to fight or sometimes a disposition to stir up a fight.
Pugnacious and combative differ from bellicose (which is sometimes given an ironic or mock-heroic turn) in applying more commonly to disposition or character; they need not, however, convey the impression of pettiness or ill nature or of readiness to fight without genuine cause, so frequently implied in quarrelsome.
Contentious frequently suggests perversity of temper and wearisome persistence in dispute.