"Many respected and highly educated historians have written and advocated the cause and purpose of the Civil War in these simple terms...The North's complete and passionate opposition to slavery and the South's complete defense of slavery was the cause and goal of the war respectfully."

==================

Of course most -if not all- of these particular historians are from the North. They promote this view for the simple fact of making the home-team look good.

When examining the motives of the war the main question should be-
Why was 'Union' valuable to the North that they would fight for it?

And the answer is in the question- The Union was valuable to the North.
A good part of their wealth was derived from economic ties with the South.
An independent South closed off that wealth.