Jeff Jacoby: Commemorating secession, with sorrow and honesty - '...It was actually Georgia's "Declaration of Causes," a 3,300-word justification of secession approved 10 days after the adoption of the ordinance, that damned Abraham Lincoln's Republican Party for its anti-slavery convictions. Secessionists in the Deep South made no bones about the fact that it was the threat posed to slavery by the incoming Lincoln administration that fueled their decision to quit the Union. Yet in recent generations, innumerable Southerners have insisted that the preservation of slavery was not why the Confederacy was formed. This revisionism, bizarre though it might seem to most Americans, has been influential in the South. So influential that the marker to be dedicated in Milledgeville this month, The New York Times reports, is "one of the first official recognitions in the state, at least in modern times, that slavery was the overarching reason for secession."...'