America loves the under dog.
That's a lot of it. Generally speaking, though, the problem is largely that the war is so Romanticized in "pop history."
No, the South probably wouldn't have won with more men (their industry was still far too inferior). In fact the worst thrashings the south typically got happened when the sides were the most even (i.e. Gettysburg and Sharpsburg/Shiloh).
No, the North wouldn't have won earlier with better generals. The ended based mostly on simple war-weariness and the south losing the battle of attrition.
And NO, the war was not fought to end slavery. That didn't come into play until half-way into it. The war was mostly a contest of two contrary socio-economic systems.
Most of what people think they know about the war is wrong. If you're interested, I highly recommend Shelby Foote's "The Civil War: A Narrative." It's all factual, but presented in the form of a narrative and written by a novelist, so it's the easiest to read history book I've ever encountered. Still, it's a hefty task as the it's a trilogy and the shortest book is almost 1,000 pages.
