In Across Five Aprils, what occurs at Gettysburg and why do post-battle conspiracy suspicions arise?

After three days of fierce combat and casualties on both sides numbering in the tens of thousands, the Union Army defeated the Confederates in what has often been thought of as the turning point in the war.  The battle, which took place in July of 1863, was one of

"unbelievable bravery and unbelievable ruthlessness; it was a clash of agonizing errors checkered with moves of brilliant strategy that lasted through three hot July days, after which the news of victory came:  A Union victory and a great one, but still not a complete one.  With broken young bodies piled high at Gettysburg and thousands of homes rocked in agony over their loss, the beaten army was allowed to with draw and prepare for still more bloodshed, while the victorious army licked its wounds and made no effort to pursue its opportunities".

Because the Union Army inexplicably refrained from using its advantage to annihilate what remained of the Confederate forces, people in the North began to wonder,

"...what does it mean?  Is there bad blood somewhere?  Is there a conspiracy among Northern generals that prevents their following up an opportunity for crushing Lee's army?"

The war was dragging on into its third year, and the people were tired and frustrated that there was no end in sight.  The failure of the Union Army to deliver a death-blow to the South while it seemingly had the chance made many wonder if there was some kind of conspiracy going on which was preventing the war from coming to a decisive conclusion (Chapter 10).

What happens at Gettysburg in Across Five Aprils? Why did suspicion of a generals' conspiracy arise?

At Gettysburg, there is a fierce and bloody battle, lasting over the course of three days, between Confederate troops led by Robert E. Lee and Union soldiers under Ulysses S. Grant. The North emerges victorious, but the cost in lives of the battle is obscene. To make things even worse, the victory is incomplete, as

"the beaten army (is) allowed to withdraw and prepare for still more bloodshed, while the victorious army lick(s) its wounds and (makes) no effort to pursue its opportunities." 

This blunder is especially frustrating, as it is not the first time it has happened. Several months earlier, at Antietam, another Union general, George McClellan, had won a telling victory but had allowed the defeated Confederate troops to retreat and regroup, to fight another day. As a consequence, a series of bloody confrontations had followed, and there was no sign that the war was ever going to end.

"With broken young bodies piled high...and thousands of homes rocked in agony over their loss...all over the North people (are) beginning to say, 'What is it - what does it mean? Is there bad blood somewhere? Is there a conspiracy among Northern generals that prevents their following up an opportunity for crushing Lee's army?" (Chapters 8 and 10).