On Cemetery Ridge at Gettysburg you can find a monument to a company of 200 Minnesotans. They probably couldn't articulate their motivations, they were probably, to the extent they cared, pro-slavery. These men attacked a formation of 10,000 Confederates, holding an otherwise fatal gap for the scant minutes needed for reinforcement. Lincoln later explained that they fought "so that government of the people, for the people, by the people shall not perish from this earth". Those that heard Lincoln probably felt he explained something they felt but couldn't say. But there weren't many of them, the company suffered 90% casualties in five minutes.
Those losses couldn't have surprised them, the company complement was the survivors of a 30% casualty rate on the prior day.
Previously George Washington caused a Continental Army, which had not been _paid_, to resign and disperse in submission to a frankly contemptible Continental Congress.
America's is government by reasoned principles, but that reason sometimes seems little more than explication of some generous impulse of freedom and justice. In the American soldier we've seen that impulse cause young men to lay down their lives, and strong men lay down arms rather than pursue their just complaints. Only later did they understand the logical necessity of their sacrifice for human freedom.
The justice of America's wars isn't always so clear, but that is not the fault of the soldier, who _must_ subordinate his own judgment to that of his countrymen lest he himself become a tyrant.
Until the lion lies down with the lamb, societies will need armies. Democracies will need armies with power to meet tyrants without using that power to become tyrants. If America's first miracle was democratic government, its second is the emergence of soldiers willing to die for it. I don't know what impulses brought forward such soldiers among us, but I suspect those same impulses today inspire our reverence for them. I know I'll always regret that I didn't take my turn at a lousy but absolutely necessary job.