One explanation for Kelly’s remarks is they reflect the views of military officers but not necessarily ordinary Americans. As the Post’s Greg Jaffe and Anne Gearan reported:

Other military officials described Kelly’s remarks as the product of a somewhat cloistered view of the conflict inculcated in military officers, but not necessarily shared by the broader public.

In fact, Kelly’s views are shared by a substantial fraction of the broader public.

Consider this graph, which was compiled by the Roper Center for Public Opinion Research from 2011 polls conducted around the Civil War’s 150th anniversary:

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With one exception these polls found more Americans cited states’ rights than slavery as the Civil War’s main cause. Even the exception — in which 42 percent said slavery was not the main reason — still shows many Americans take a position not dissimilar from Kelly’s.

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A more recent poll shows the same thing. In July 2015, a McClatchy-Marist poll asked “Was slavery the main reason for the Civil War, or not?” Just over half (53 percent) said it was, while 41 percent said it was not. Among Republicans, opinion was more narrowly divided: 49 percent yes and 45 percent no.