“Why does the author consistently, insistently and repetitively refer to the War of the Rebellion as, the War of 1861?”
You need to reread the article. In 1861, everyone knew that states had a right to secede. The right to secede was not rebellion; it was classified rebellion to justify the carnage.
And by the way, what was the point of the author in resurrecting HL Menken just to have him mIquote Lincoln and then castigate Lincoln for making a statement he never made?