First, I am not totally sure you understand what anarchists are talking about when we use the phrase social war. Here are a couple links, both for you, and so that all these “wtf? social war?” questions are easily found:
I am personally hesitant to use the term social war, at least in contexts where the people I was addressing didn't know me well enough to share an understanding of what I mean when I do use it. As is hinted at in the answers to the first question above, the social war is sometimes hard to define, or the definition varies from person to person. I do think that, as Sabotage says in the answer to the second link, that social war is a way of broadening the plane of contestation beyond the rhetoric of class war.
As an anarchist living in a world defined by the state, capitalism, patriarchy and domination a part of who I am (as someone who opposes all these things) is antagonistic to the social order, and to the extent that I live in line with my beliefs, conflict will happen. Left as an isolated individual, I am an outcast, rebel, crazy, anti-social, outlaw, sociopath, or just plain bad. Luckily, I don’t exist in isolation, and there are many others who feel similarly (or quite differently) disenchanted with the current state of affairs. To the extent that we find common goals in moments of rebellion, and then try to expand these moments into a broader state of conflict with all these things we hate, there are the beginnings of social war.
Part of why I question your understanding of what we mean by social war is that you seem to view anarchists as competing for power. We are, in fact, about destroying the sort of power that you speak of, and the anarchists I respect use the term “politics” only in a negative sense. That is actually an important distinction between anarchists and communists: communists seek power so as to (supposedly) “dissolve the political question” through collectivized labor, management and distribution of wealth, and an eventual withering of the state. Anarchists see this promised dissolution as a canard, seeking instead to be active agents in its demise. Related, but on the opposite side of things, if we just chose to join unions and vote to affect change, hoping to slowly garner greater consensus, we wouldn't be anarchists any longer, we’d be democrats.
Lastly, on the question of strategy and nihilism: Social war isn't a strategy, so much as a way of understanding and contextualizing various conflicts on a broader scale. Sometimes these things will be clearly related; sometimes they might even seem to be in conflict with each other. Each of these particular situations and conflicts will require its own strategic assessment based on all sorts of variables that concepts like the social war can’t begin to account for. This goal of confrontation and destruction doesn't end after the revolution (the idea of a revolution being another problem that can be explored). I personally would never assume that my goals as an anarchist will match up with those of most of society, and I expect there will be continued conflict because of this, and there will always be a need to destroy the existing social order. So sure, maybe it is nihilism, I feel fine with that, though there are other social warriors who would reject that.
Final note: I didn't really address your quotes from James Madison and Carl Schmidt because really? The father of the constitution and a nazi cited as refutation of the social war? That is either the best trolling ever, or a total lack of understanding of what anarchists are about.