By tradition, wars have been fought between states. In the glory days of "honorable" warfare, armed clashes was preceded by official declarations of war, at times even by agreement on where and when to meet. Those days are long gone. The practice of formally declaring war was made obsolete by World War II and the benefits of surprise attack have since totally eclipsed any notion of honor in the combat-starting business.
More recently, and more fundamentally, warfare has entered a stage where the parties engaged are no longer easily recognizable as states. Some security experts have even gone so far as to say that the era of war between states has come to an end and that this is a good thing. The latter is a very dubious claim.