Slavery was the catalyst for the civil war. There are many similarities between slavery and religion.The Civil War, WW1 and WW2 were not religious wars.
The cause of World War 1 was a visit to Serbia from Austria's Archduke where he was assassinated by one of many angry Serbians who was mistreated by the Austrian Government. They felt mistreated because the Austrian Government enforced higher taxes to pay for churches. On the Western Front there was certainly no religious aspect to what went on. However, the Western Front was NOT the only front in the War. Elsewhere, there was fighting in territories that had formed part of the Ottoman Empire, and while WW1 was going on there was religiously-motivated genocide. The Ottomans killed hundreds of thousands of people who were members of the Assyrian Community, whose religious affiliation was mainly Christian.
Hitler was an extreme christian and made many references to his Christianity during his speeches during WWII.
Slavery is still going strong throughout the world.Slavery was universal in the ancient world.