No, the Civil War was about slavery.
Some of the Southerners may have fought to save slavery, some for their state, others for some other reason.
these two statements directly contradict eachother. the political considerations of the man in charge do not render obsolete the motivations of the people actually dying while following his orders. if a war is about one thing to politicians who start it, and about another thing to the soldiers fighting it, then it is about all those things, not simply about whatever the winner's politicians said it was about.
Lincoln stated explicitly, so as to leave no confusion, that the war was not about slavery in and of itself:
That said, the Confederate flag doesn't mean what most Northerners think it means anymore. Speaking from the perspective of an urban Northerner who used to assume that anyone with a Confederate flag is a hick, it really is just a symbol of Southern pride to most people. I learned that after just a week in Tennessee on a spring break training trip for rowing. There were very nice, very pro-America, non-racist people down there who had Confederate flags out. When asked why, they said it's their way of showing pride in their Southern culture, and the South definitely has its own culture.
so, you had an erroneous opinion and perhaps a false sense of moral superiority about a large group of people who were geographically distant from you. rewind this 100+ years when they had much less means of travel and sharing information, making it much harder to dispel stereotypes and assumptions in the way that you did yours. You still think it was all about slavery? And that the way southerners feel about southern pride wasn't just as much a factor back then?
the main reason the issue survives is because people prefer to take the easy way out and paint the issue in moral absolutes that favor the winner (well, or the loser if you say slavery was irrelevant). the federal government never has to apologize for forcibly retaining those who do not want to be a part of it, or promise not to do it again, as long as it pushes the public's attention to moral issues which cast the past losers in an unfavorable light. "we weren't fighting to maintain a monopoly on power, we were fighting to free slaves..." (the implication, at least).
there's no dodging the fact that slavery was a central issue, but for it to be the defining issue of the war would require that most southerners who fought, were putting their lives on the line for the right to own slaves; not out of southern pride. If it is true that most of them fought for the latter and not the former reason, then the civil war was like most wars in that it was fought because two groups of people developed profoundly different ethos and culture because their geography and economy led them to develop that way, and they became too divided to tolerate eachother.
anyway, it's not conducive to 'the union' that so many in the north believe what is so easy to believe: that the war was a simple moral issue and the winners were right. that kind of generalization is the strongest evidence that other factors other than simple moral deficiency caused the war. if the north had been full of land suitable to crops like cotton, would they have developed a different economic path and less slave based culture? if they hadn't been feeding off of the success of the southern slave based economy, would they have been powerful enough to fight them? I'm glad slavery was abolished, but let's not pretend that either the north or the south are objective about the moral reasons behind the whole thing. Maybe Lincoln was right to fight to preserve the Union, considering that the divisive issue of slavery and the general cultural division may have made war inevitable even if he had allowed a peaceful secession. But scapegoating the south with oversimplified generalizations about their motives for fighting and dying is only going to lead down the exact same path and undo what he fought for.
tl;dr: the reason for any war is based on why the average participant is fighting it, not just what politicians say, and oversimplifying breeds resentment.