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.
Eventually, Jiran's son Kadaman was executed for demanding an end to the Red Raids. This resulted in Prince Avad fleeing the Sundom, forging an alliance with Oseram freebooters. After months of planning, they launched an assault on Meridian, overthrowing Jiran and ending the Red Raids. However, many Carja still supported Jiran, believing that as the speaker of the Sun, even his most heinous crimes were justified. During the battle, approximately half of the tribe (including Jiran's youngest son Itamen and wife Nasadi) fled the holy city to Sunfall in the northwest. Calling themselves the Carja in Shadow, they deemed themselves the true Carja, anointing Itamen as their Sun-King.
By the third year of Avad's reign, the war was trapped in a tenuous stalemate: the Shadow Carja lacked the resources to feed their people, let alone retake Meridian. On the other end, Avad was unwilling to launch an invasion on Sunfall, believing that the tribe had already suffered enough carnage.
The Carja tribe is divided into two factions, the Carja in Sun, known simply as the “Carja" or "Sun Carja," and the Carja in Shadow, more commonly referred to as the Shadow Carja.
Dervahl, an Oseram warlord bent on revenge against the Carja, captured the Oseram Vanguard captain Ersa and proceeded to frame the Shadow Carja for murdering her. Had his deception not been discovered by Aloy, the outrage at Ersa's "death" would have forced Avad to break the ceasefire.