The essential conflict at the heart of Fallout is the contradiction between the human drive towards community and interconnectedness and the opposite drive towards alienation and self-superiority. Civilization reasserts itself because human beings are social animals with social values, who care about the world beyond their immediate families. They have desires informed by material needs, which is why "war never changes" in the first place. People desire to have what is beyond their means through fair exchange, and those desires lead to conflict. There is no "war" in the traditional sense featured in the first two Fallout games, because the actual conflict is an unseen war being waged on humanity by "alien" powers who want to reshape the world according to their own personal ideals. They are not threats which are OF the world as it is, reconstructed by those who live in it. They're threats from the old world, echoes of the instruments and ideologies which caused the Great War.
In every Fallout game, even the Bethsofts, the old world is defeated so that the new world can live. In Fallout TV the old world resets everything back to Square 1 because it turns out they had an "I Win" button all along, and no player characters were born between the events of New Vegas and Fallout 4 so anything can happen.