One of the main themes could be power struggle. Angels might fight over who gets to lead or have more influence in their celestial realm.
The theme of redemption could also be present. Some angels might see the civil war as a chance to atone for past mistakes or sins. They could be fighting for a cause they believe will bring about a better, more just celestial order. Or perhaps some angels on the wrong side of the war might seek redemption as they realize the error of their ways during the course of the conflict.
The main themes include sacrifice. In the context of the Civil War, many soldiers sacrificed their lives, and this novel may focus on those selfless acts. It might also touch on the theme of identity, as the war forced people to re - evaluate who they were, whether they were from the North or the South. Additionally, the theme of brotherhood in arms could be present, despite the differences between the two sides, soldiers often had a bond with their fellow fighters.
I'm not entirely sure without reading it specifically, but I would assume there are soldiers on both the Union and Confederate sides. There might be a brave Union officer who is leading his troops into battle. And perhaps a Confederate soldier who has a family back home that he's fighting for.
There could be an archangel as a key character. Archangels are often depicted as powerful leaders in angel lore, so in a civil war, one might be leading a side of the conflict.
In 1895 civil war novels, the theme of national identity was often explored. The war was a struggle between two different visions for the United States. So, novels might show characters grappling with what it means to be an American, whether it was loyalty to the Union or to the Confederacy. Also, the theme of brotherhood (and in some cases, the breakdown of it) was present. Soldiers formed strong bonds with their comrades, but the war also pitted brother against brother in some families.
One main theme could be the brutality of war. In civil wars, like the one depicted in the novel, the violence among people who were once compatriots is often extreme. Another theme might be the search for identity. Characters may struggle to define themselves in the chaos of the civil war.
One main theme is the destruction of war. These novels often show how the civil war brought devastation to the land, cities, and lives of people.
One of the main themes is loyalty. Captain America and Iron Man have different views on the Sokovia Accords, which tests their loyalty to each other and to their own beliefs. Another theme is the cost of heroism. The heroes have to face the consequences of their actions and how their actions affect the public. There's also the theme of freedom vs. regulation. Captain America believes in the freedom of the Avengers to act as they see fit, while Iron Man thinks some regulation is necessary to prevent more destruction.
One of the main themes is often sacrifice. Soldiers sacrifice their lives, families are torn apart, and people give up their previous ways of life. For example, in 'Gone with the Wind', many characters lose their loved ones and their wealth due to the war.
One of the main themes could be the contrast between the chaos of war and the hope that Christmas brings. During the Civil War, Christmas might have been a time when soldiers on both sides thought about home, family, and peace, even in the midst of battle.
The main themes in Christian civil war novels include forgiveness. As people are caught up in the war, they have to find it in their hearts to forgive their enemies, which is a very Christian concept. Another theme is perseverance. Characters persevere through the hardships of war, relying on their Christian faith. And the theme of spiritual growth is also present. The civil war is a crucible in which characters' Christian beliefs can either wither away or grow stronger, and novels often explore this journey of spiritual growth.