The officers did not turn against any nation. At the time, the union was considered a Republic of Republics, and the sovereign states were sovereign. As they had acceded to the Union, states seceded from the Union. The sovereign state, of which they were citizens, withdrew from the Union and no longer considered itself part of the United States of America. Their allegiance was to their sovereign state, not to the union of states.
The soldier could have fought honorably for North or South, just as a soldier in WW2 could have fought honorably for Germany or Japan. The soldiers are not the aristocrats and politicians who create the wars. Professional fighters, after beating on each other, often wind up displaying respect for each other. Soldiers fighting on opposite sides can also respect each other.
During the Battle of Kennesaw Mountain, Georgia, an unlikely truce took place. Lt. Colonel William Martin, commander of the 1st and 15th Arkansas, saw that flames were roasting many Federal wounded. Placing his handkerchief on a ramrod, Martin jumped onto the parapet to offer a truce. "Come and remove your wounded; they are burning to death, we won't fire a gun until you get them away. Be quick!"Then, while gunfire raged over the rest of the battlefield, a merciful quiet came over this little part of the mountain. Men in gray helped men in blue to save the wounded.
After the burned area was cleared and the fire put out, a Federal major brought Colonel Martin a gift of appreciation -- matched Colt revolvers. And then both sides went back to killing each other!
Source: A Civil War Pocket Reader, Compiled by John Zwemer, p. 107; attributed to Ronald H. Bailey, Battles for Atlanta, Alexandria: Time Life Books, 1985, p. 71.
The first paragraph I disagree with. From the founders on, the principles were of an American nation, not 13 nations. While I would argue also that the civil war was actually the last conflict of the revolutionary war, the Mexican war was a war fought not on the behalf of Virginia or Maine, but the United States.
The rest of your post sounds good to me. The real tragedy was the Civil War was a war of Americans vs. Americans.