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.
One of the main themes is the conflict between personal freedom and government control. The superheroes are divided on whether they should be regulated by the government. Another theme is loyalty, as friends and allies find themselves on opposite sides of the conflict.
One common theme is division. In a 2nd civil war novel, the nation is often split along ideological, political, or social lines. Another theme is power struggle. Different groups fight for control over the country. Also, there is the theme of sacrifice. Characters may have to sacrifice their personal beliefs, relationships, or even their lives for the cause they believe in.
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.
Survival is a major theme. In the midst of a civil war and a zombie outbreak, characters have to find ways to stay alive. They need to find food, shelter, and protect themselves from both the living enemies in the civil war and the undead zombies.
One of the main themes is the concept of courage. The protagonist's journey in the civil war is filled with moments where he has to face his own fears and redefine what it means to be brave.
One main theme is loyalty. Characters often have to decide where their loyalties lie, whether it's to their family, their social class, or a particular side in the civil war. For example, in some novels, a noble might be torn between supporting the king or the parliamentarians because of his family's long - standing ties to the monarchy but his own beliefs about governance.
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.