Where It All Goes Down
Gettysburg, Pennsylvania, June 29-July 3 1863
At the time of the battle, Gettysburg was a quiet college town—actually, it still is today. It's surrounded by rolling Pennsylvanian farmland, a Lutheran seminary, and some hills and ridges, which were totally important in the battle.
There's one more crucial detail about Gettysburg: it's in the North. Lee's army decided to turn the tables on Lincoln: instead of playing defense in the South, they ventured north into Pennsylvania, hoping to force a Union defeat. Gettysburg is the high water mark of the Confederacy—the place where it came closest to fulfilling its dream of secession… before watching that dream get totally dashed.
Since this is a book about a battle, the details of the landscape are crucial: whoever controls the high ground stands the best chance of winning. To illustrate just how important this is, when Lee orders an advance across open ground toward the Union position up on Cemetery Ridge on the last day of the battle, it becomes one of the most famous defeats in history: Pickett's Charge, basically a symbol for foolhardy and doomed bravery.
Chamberlain's fight to secure Little Round Top is another example of this point. By keeping the hill, Chamberlain made sure that the Northern troops had a commanding position over the whole battlefield.