What started the Civil War?

Nikki Haley stumbles on a question that your average 5th grader should be able to answer.

During a town hall in New Hampshire on Wednesday evening, Nikki Haley was asked, "What was the cause of the United States Civil War?"

Yes, it is a strange question for a presidential town hall, but it shouldn't have been a question that stumps a presidential candidate. 

And yet, Haley stumbled. 

Watch: