Well, like all analogies, there are limitations. On the most obvious side, an international war is distinct from a Civil War — after all, we didn’t annex Germany after WWII. Another important distinction is a defensive war versus a war of aggression — who started it at Fort Sumter aside, The Battle of First Manassas could have ended the war, had the South simply marched on Washington D.C. and conquered the capital of the North. A more appropriate analogy might be “Man in the High Castle” style victory for the Nazis against the U.S. — not because of the morality of either side, but simply because of the clear aggressor in each case. And last, but not least, there was no precedent of peaceful resolution to severe anti-semitism like in Germany — western governments had a long history of the peaceful end of the institution of slavery, on the other hand. If one could make the case that the jews could have been freed from concentration camps through peaceful means rather than violent ones, then perhaps the analogy would hold.
As well, even for all the atrocities of Heinrich Himmler, one would be hard pressed to see him as any less evil than say, William Tecumseh Sherman…who happened to serve on the Union side. And one would be hard pressed to categorize Robert E. Lee as a genocidal sadist in the same way Himmler was.
In any case, even if one could proclaim 90% of the German population irredeemably evil in 1942, how did we decide to treat them after their defeat? We certainly learned from WWI that punishing sanctions and economic devastation wasn’t a road to peace — and what was left? The Marshall Plan. Reconciliation.
And even today, we don’t have any massive push to destroy and tear down the various WW2 statuary and memorials in Germany. Of course, as part of Germany’s crackdown on free speech, and as a whitewash of their sordid history, they did scrape swastikas off of a number of memorials, even as Nazis continued to hold power in the post-WW2 government. It seems to me that it would have been more honest for them to have left the swastikas in place as a reminder of their shame.
That all being said, do the German dead of WW2 deserved to be mourned even though their cause was unjust? I think simply humanity requires that we answer that question in the affirmative.
