All wars end, but someone must bring them to an end: someone in authority must order the men to stop fighting, or the fighters themselves must decide to stop fighting even if doing so requires that they disobey standing orders. Either way, someone makes a decision to bring the war to an end, and we may presume (in conformity to the precepts of methodological individualism) that the actor makes the decision only because he believes that it serves his interest, however he may conceive of that interest. In general, in our day nations do not go to war spontaneously, nor do they lay down their arms spontaneously. National leaders make those decisions, and they make them in their own interest.
Any other view is romantic and obscurantist, notwithstanding the torrents of propaganda by which leaders and their court intellectuals attempt to represent themselves as "servants" of the nation, as embodiments of "the national will," or as executors of "the public interest." Even if political and military leaders were inclined to put the public's interest ahead of their own, they would have no way to identify such a foggy and multifaceted entity. Each individual has many interests; different individuals have different sets of interests; and nobody has discovered a defensible method of aggregating all these interests into a single "social interest."