The era of the Civil War was a time of strongly held beliefs, deep emotions, and grandiose actions. By today's standards, some of it may seem trite or excessive, but for that time, it was sincere. Some of the themes in this area are
Class structure: Class distinctions are very strong, especially in the South. It is an aristocratic structure where gentlemen are an exclusive club, and to be a Virginian is the best. They are refined, wealthy, powerful, and ruled by a code of chivalry. Honor is everything, and a man would die to save or recover his honor. This theme figures prominently in many of the Southern characters in the story, especially Armistead, Garnett, and Pickett. It is also something the Englishman, Fremantle, recognizes at once and admires for its closeness to England.
The North is just the opposite. The class constraints of the Old World are despised and rejected. Instead, the culture is composed of immigrants seeking freedom from that world. They want only the chance to be judged for who they are and what they can do, not who their father was. The character of Kilrain portrays this very strongly, as does Buford, whose comments and observations about "gentlemen" and their methods of battle, are laced with sarcasm.
Glory of battle: Men of this time speak with great emotion of the glory of battle. They recall fondly the Charge of the Light Brigade. They revel in saber charges and speak passionately about the beauty of thousands of brave men in formation marching to their deaths, with banners flying and music playing. They are fearless men performing daring exploits for the glory of their cause and their homes.
Rebel Yell: The Confederates have a blood-curling yell they use as they attack. It is meant to inspire the men on to glory and strike terror into the hearts of their opponents.
Flags: A point of honor is the flag or pennant carried by a particular group in battle. The flag helps to keep things organized during the chaos of a fight. Men can look to the flag and see where they are supposed to be. But it is also an emotional tool, a metaphor for success or failure. Men would die rather than let their banner fall, and it is a great loss of honor to have one's banner captured. It is an equal honor to capture as many of the enemy's flags as possible.
Music: Music was used in camp as well as in battle. In camp, there might be sentimental singing and music, bringing thoughts of home, the past, and friends long gone. There are also the times with visiting relatives and polka bands, giving the camp a carnival atmosphere. Bugle calls and drums are used for marching and in battle to keep men in ranks, let them know where their group is, and what they are to do next.
Strategy: Strategy is mentioned frequently throughout the book. Lee prefers Napoleonic tactics, which is the currently favored method of fighting in the world, and ties into honor. One does not gain glory or honor sitting behind defensive works. Longstreet takes up the opposite position, preferring defensive strategies that make the enemy come to him. He advocates the use of trenches, something Lee refuses to do. Lee sees the Napoleonic method as an extension of the man, and that is the only way he will fight. Most of the Southern officers and Fremantle agree with Lee.
Interestingly, the Union cavalry commander, Buford, seems to agree with Longstreet's beliefs. Both of the men have served out West and value defensive tactics as much, if not more than, the flamboyant charges of offensive warfare. To this day, there remains the question of whether the loss at Gettysburg was due to Lee's poor judgment and refusal to consider a different strategy, or Longstreet's lack of commitment because he disagreed with the strategy Lee was using.
God's will: The book has a strong element of "predestination" and of "God's will at work" in the battle. Lee speaks frequently of forces beyond all of them directing the battle and that all of it is in God's hands.
It also has the element of divine retribution for a sacred oath broken. All the Confederate officers who had earlier served in the Union Army took an oath to protect and preserve the Union. That oath was broken when they took up arms for the Confederacy. In discussions between Lee and Longstreet, you see that they harbor doubts about whether they were right to break that oath, and whether that betrayal will cost them the war. Even the wife of General Pender predicts her husband will die because the Confederates have moved onto Union soil, and the Lord will avenge that.
Other elements to watch for in the book include Shaara's use of character, relationships, and irony, as well the themes of command style conflicts, command mistakes, morale in the two armies, the effect of chance and circumstance in the battle, and the issue of "good ground."