IR specialists are confounded today by the actions of nations not following their national interests. This is especially required, they say, in cases of war. But now and in the future, war will happen for a different, non-rational reason.
Instead war will be exploratory. It will be waged to shake things up. Because the postmodern age offers no grand ideals, not even nationalism, to fight for (yes I know of Ukraine so don't contradict yet). There is little to guide big moves in a postmodern world. Random shocks can arrive but they will not be new. Progress as Hegelian rationality is well done.
Postmodernism is a fast world but a slow one too. Change becomes the result of accretion of mass, of events unrelated which gather but which press history forward in no particular direction. Postmodernism condemns us to repetition of familiar events that pop out of the mass briefly (witness the terribly derivative Hong Kong occupy movement).
Wars are now efforts to effect desired change in an era that works against such desire. In the face of the ongoing, massive accretion of many, less weighty, events, then wars will be waged to shake loose the status quo in a favorable direction. But be assured that national interests will not be served by it today.