What is the greatest myth about the causes of the Civil War?

The Civil War wasn't about slavery.

The most widespread myth is also the most basic. Across America, 60 percent to 75 percent of high-school history teachers believe and teach that the South seceded for state's rights, said Jim Loewen, author of "Lies My Teacher Told Me: Everything Your American History Textbook Got Wrong" (Touchstone, 1996) and co-editor of "The Confederate and Neo-Confederate Reader: The 'Great Truth' about the 'Lost Cause'" (University Press of Mississippi, 2010).

"It's complete B.S.," Loewen told LiveScience. "And by B.S., I mean 'bad scholarship.'"

In fact, Loewen said, the original documents of the Confederacy show quite clearly that the war was based on one thing: slavery. For example, in its declaration of secession, Mississippi explained, "Our position is thoroughly identified with the institution of slavery — the greatest material interest of the world … a blow at slavery is a blow at commerce and civilization." In its declaration of secession, South Carolina actually comes out against the rights of states to make their own laws — at least when those laws conflict with slaveholding. "In the State of New York even the right of transit for a slave has been denied by her tribunals," the document reads. The right of transit, Loewen said, was the right of slaveholders to bring their slaves along with them on trips to non-slaveholding states.

Explanation:

the answer is they believed george iii would never give them their freedom.