On the landing between the first and second floors of the Boston Public Library, twin marble monuments pay tribute to Massachusetts men who fought in the Civil War. The short pillars are capped by lions. The text, honoring the Second and 20th Infantries, is simple, noting that the monuments were given by the people of Boston in honor of those who fought, those who died. The battles in which the units participated are listed on each monument.

The list for the Second Massachusetts Volunteer Infantry includes Winchester, Cedar Mountain, Antietam, Chancellorsville, Gettysburg, and Sherman's Carolina Campaign during the last months of the war. The Second Massachusetts knew bloodshed in a war in which 620,000 people died.

Most of the Civil War was fought in the Confederate states or border states like Maryland and Kentucky -- with Gettysburg, in southern Pennsylvania, a great exception. Most of the historic war sites and post-war memorials are in the South. It's probably true that those whose ancestors fought for the confederacy have more frequent contact with war sites and memorials than those who ancestors fought for the North.

A few years ago, the library exhibited letters pre-war New England women wrote attacking slavery. The women could not vote, could not hold public office. But they could make their views known to public officials, neighbors, relatives and complete strangers through the pages of newspapers. One of the women described slavery as "a hissing." What a vivid, compelling use of a verb as a noun.

Over the years, I have written columns about various aspects of the Civil War. These pieces have not provoked controversy except when I have referred to the primary cause of the war -- slavery. My interpretation of the cause of the war, now shared by most competent historians, inflames many of those whose ancestors marched under the stars and bars. They tell me the war was fought for states' rights, and in some cases go on to condemn me as a Yankee scalawag, coward or dog. One incensed son of the Confederacy, whose great-great-great grandfather Beauregard fought in gray, threatened to horse whip me should I ever repeat the calumny that slavery caused the war. Perhaps he dressed as Simon Legree for Halloween.

Slavery was explicitly protected by the Confederate Constitution, the South's governing document. Southern statesmen, economic theorists, political theorists, and journalists believed slavery was essential to the antebellum way of life and deserved protection as a property right through violence if necessary. No slavery, no confederacy.

As Princeton historian James McPherson pointed out, Confederate Vice President Alexander H. Stephens, told a Savannah, Georgia, audience on March 21, 1861, slavery was "the immediate cause of the late rupture and the present revolution" of Southern independence. Stephens continued by voicing his his belief the Confederacy rested "upon the great truth that the negro is not equal to the white man; that slavery, subordination to the superior race, is his natural and moral condition."

Many years ago as a graduate student at Duke University, I asked the professor who taught undergraduates the Civil War what surprised him most about his students. The professor, an elegant Southern gentleman, laughed and replied "There is always some student -- usually from Georgia -- who just can't believe the North won the war."

Tennessee Williams said "The human heart is a stubborn organ." So is the human brain. People find it extremely difficult to admit they are wrong. This is not only true for revered ancestors, as in the Civil War example, but in contemporary politics. Look at the people who still believe Barack Obama is not a citizen. Or that fewer Americans are insured under the Affordable Care Act than before it became law. Or that the unemployment rate has decreased, not increased, during the Obama years.

The sentence "I was wrong" may contain the three most difficult words to say in the English language. And some people never say them.

Michael Carey is an Alaska Dispatch News columnist.