The First "Modern" War?

The Civil War is often considered the first "modern" American war for a variety of reasons. What was significant and wholly new about the war America waged war between the North and South during the Civil War? Think in terms of technology, economy, and tactics. Also, how did the fighting of the war differ from the its beginning to its end?
Civil War one side (meaning the North) "was wholly and eternally right," while the other side (meaning the South) "was wholly and eternally wrong." I might cite those on the Southern side of the great controversy, equally sincere and fully as able, who would have been glad to persuade posterity that the North was "wholly and eternally wrong"; that her people waged war upon sister States who sought peacefully to set up a homogeneous government, and meditated no wrong or warfare upon the remaining sister States. These Southern leaders steadfastly maintained that the Southern people, in the exercise of the freedom and sovereign rights purchased by Revolutionary blood, were asserting a second independence according to the teachings and example of their fathers.
      But what good is to come to the country from partisan utterances on either side? My own well-considered and long-entertained opinion, my settled and profound conviction, the correctness of which the future will vindicate, is this: that the one thing which is "wholly and eternally wrong" is the effort of so-called statesmen to inject one-sided and jaundiced sentiments into the youth of the country in either section. Such sentiments are neither consistent with the truth of history, nor conducive to the future welfare and unity of the Republic. The assumption on either side of all the righteousness and all the truth would produce a belittling arrogance, and an offensive intolerance of the opposing section; or, if either section could be persuaded that it was "wholly and eternally wrong," it would inevitably destroy the self-respect and manhood of its people. A far...