This is definitely designed to be provocative (Vicksburg and the the western fighting a mere "sideshow?" Don't think so). As such, he starts with a common conclusion about the battle (the feds lost, but for the first time showed they could go toe-to-toe with southern cavalry), and then expands it.

What's interesting with this piece is that he supports his position with quotes from participants, made just after the battle. The quotes tend to support his position: not that it was a tactical Union victory -- he admits it wasn't -- but that the balance of power began to tip toward federal cavalry there. I don't agree that he concludes it was a Union victory in any purely military sense. He concluded that is was a Union "moral' victory because his evidence tends to show that's what a large number of Union troopers thought. Were they justified in thinking so? I don't know.