The Carja Civil War is an ongoing conflict within the kingdom of the Carja tribe, the largest tribe in Horizon Zero Dawn. The tribe is split between religious hardliners who are loyal to the previous Sun-King, Jiran, and those who support his son and the Sundom's current ruling monarch, Avad. The war was sparked by a crisis of succession and is being fought over a disagreement about the direction of the tribe. Tensions within the tribe were growing for years prior to the death of the 13th Sun-King due to growing disapproval of the Red Raids, and the split considerably worsened following Jiran's death.
During the reign of the Mad Sun-King Jiran, the machines throughout the Sundom became increasingly more hostile towards the Sundom's human population in a phenomenon that came to be known as the Derangement. Many Carja believed the change in the machines' temperament was some kind of punishment from the Sun god. After years of prayer did nothing to reverse the Derangement, Jiran revived the long-abandoned Carja ritual of human sacrifice in an attempt to appease the gods.
However, by the fifteenth year of his reign, the machines' hostility continued to grow and, even worse, new and more aggressive combat-driven machines began appearing throughout the Sundom. Jiran reacted by increasing the cruelty of his ritual human sacrifices. His regime began sacrificing their own tribe members who they suspected of wavering in loyalty. Eventually, Carja soldiers raided neighboring tribes and kidnapped hundreds of people for the purpose of slavery or sacrifice in a series of invasions that became known as the Red Raids.
During the events of Horizon Zero Dawn, the two sides have entered into a tenuous ceasefire. The war has entered a stalemate because the Shadow Carja are too impoverished and weak to mount a formidable defense and Avad is unwilling to wage war on those at Sunfall, particularly because many are his friends and family.
The Carja tribe is divided into two factions, the Carja in Sun, known simply as the “Carja,” and the Carja in Shadow, more commonly referred to as the Shadow Carja.