The Civil War was about slavery, folks

Unfortunately, Gen Xers younger than me seem to have believed the Reagan/GOP propaganda - as a new Pew poll notes, while 48 percent of Americans overall say it was primarily about states rights:

Young people are more likely than older Americans to say that the war’s main cause was states’ rights – 60% of those younger than 30 express this view, the highest percentage of any age group.

Paging Tony Horwitz. Confederates aren't in the attic, they're at PlayStations.

At the same time, the poll says fewer people support public officials praising Confederates. But, we know people often give answers they think they "should" give in such cases.

That said, a NYT Opinionator column notes that we have the historical records, in this case from secession debates in Virginia, to show it was indeed about slavery:

The language of slavery is everywhere in the debates. It appears as an economic engine, a means of civilizing Africans, an essential security against black uprisings and as a right guaranteed in the United States Constitution. Secessionists and Unionists, who disagreed on so much, agreed on the necessity of slavery, a defining feature of Virginia for over 200 years.

The language of slavery, in fact, became ever more visible as the crisis mounted to the crescendo of secession in mid-April. Slavery in Virginia, delegates warned, would immediately decay if Virginia were cut off from fellow states that served as the market for their slaves and as their political allies against the Republicans. A Virginia trapped, alone, in the United States would find itself defenseless against runaways, abolitionists and slave rebellions.

Read the full column.