The Liberation of Meridian

The Liberation of Meridian, referred to as the Fall of Meridian by the Shadow Carja, was a battle that began the ongoing Carja civil war in Horizon Zero Dawn. The assault, launched by Avad and the Oseram Vanguard on Meridian, brought about the death of Sun-King Jiran and the end of the Red Raids.

Events

Red Raids

Main article: Red Raids During the reign of the 13th Sun-King Jiran, the machines started becoming progressively hostile towards humans. Interpreting this phenomenon as a sign of the Sun's displeasure, Jiran believed that blood sacrifice would calm the machines' anger. He ordered the raiding of nearby tribes for victims to sacrifice in the Sun-Ring. This progressed into the decade-long Red Raids. Despite the slaughter having no effect on the machines (in fact, they became even more dangerous), Jiran continued to order human sacrifice. Like the machines, Jiran became increasingly aggressive, and began executing anyone who dared to protest him. It reached the point where Kadaman, his eldest son and heir, was executed for merely demanding an end to the Raids.
The night of Kadaman's death, Jiran's second son Avad fled to The Claim with his honor guard, knowing he would be deemed a traitor. In the Claim, he found an old friend: a freebooter named Ersa, who had been made a palace slave after surviving the Sun-Ring. During her time as a slave, she befriended Avad, who eventually helped her escape servitude. Once reunited, Ersa, along with her brother Erend, agreed to join forces with Avad and end Jiran's brutal reign.

Preparations

Ersa's connections with Oseram warlords and freebooters helped her and Avad form an army. After months of preparation, Avad and his forces began their march to Meridian. Despite being marked for death, Avad was still of the Radiant Line, and was therefore a legitimate heir to the throne in the eyes of many Carja. While Avad knew that Jiran's forces would protect their king at all costs (even at the expense of Meridian's people), he hoped this birthright would at least prevent an all-out war from erupting in the holy city.
As Carja religion hailed the Sun-King as the sun's representative, the Carja initially believed that Jiran's rank alone justified his actions. However, as the atrocities continued and only increased in brutality, support for Jiran began waning, replaced by disgust and shame. Therefore, when news of Avad's approach spread, many soldiers defected to the banished prince's side.

The Battle

It seems that Jiran was not initially concerned about the invasion: even as the assault began, he expressed his belief that the strong were being "beset upon by the weak". Nevertheless, he had kestrels and the city guard placed at the city's walls, ready to shoot down any who dared march on the city.

Aftermath

Ascending to the rank of Sun-King, Avad brought an end to the Red Raids. The freebooters who marched with him became an elite group called the Vanguard, with Ersa as their captain.