Contemporary historians overwhelmingly agree that secession was motivated by slavery. There were numerous causes for secession, but preservation and expansion of slavery was easily the most important of them. The confusion may come from blending the causes of secession with the causes of the war, which were separate but related issues. (Lincoln entered a military conflict not to free the slaves but to put down a rebellion or, as he put it, to preserve the Union.) According to the historian Kenneth M. Stampp, each side supported states' rights or federal power only when it was convenient for it to do so. Stampp also cited Confederate Vice President Alexander Stephens's "A Constitutional View of the Late War Between the States" as an example of a Southern leader who said that slavery was the "cornerstone of the Confederacy" when the war began and later said after his defeat that the war had not been about slavery but states' rights. According to Stampp, Stephens became one of the most ardent defenders of the 'Lost Cause' myth.