The first season of House Of The Dragon outlined the events in King Viserys' reign that led to the civil war between his daughter Rhaenyra and son Aegon.
Viserys himself played a part in the timeline that would lead to tensions within his family. However, it was largely the actions of his wife Alicent and daughter Rhaenyra that would divide the realm and the powerful Targaryen house. These key events throughout the years paved the way to the Targaryen civil war, pitting house against house and sibling against sibling.
This article contains spoilers for House of the Dragon.
10 Aemma And Baelon's Death
At the beginning of the season, the death of Queen Aemma and her son Baelon sets up the story for the rest of the turn of events. After Viserys has lost his wife and seemingly the last chance he had to have a male heir, his perspective changes.
Once Viserys disinherits his brother Daemon for mocking his son as "Heir for a Day", he has to secure his succession. With his wife dead, and another child lost in childbirth, he had little prospects at the time. It was this event that made him realize how much of a fool he was overlooking his only child.
9 Rhaenyra Is Named Heir
Viserys could have remarried and tried to have another child before naming another heir. However, with only one child after nearly a decade on the throne, the king knew he had to make a decision that would make his succession clear if something were to happen to him when he still didn't have a male heir.
While Viserys was making a thoughtful decision in naming his oldest and only child heir to the throne, it was a shock for the whole kingdom. Had she stayed his only child, there likely would have still been those that challenge her abilities as ruler, but it would have been less of a challenge without any other heirs with a claim.
8 Aegon's Birth
Viserys remarrying was inevitable as it was his duty as king, but his actually producing a male heir was a hit or miss. However, his decision to name Rhaenyra his heir became more complicated after the birth of Aegon II.
The boy was still a baby when others in the kingdom began to question when Viserys would name Aegon his heir. The king chose to ignore these inquiries and decided he would not supplant Rhaenyra regardless of his male heirs. Regardless if his people loved Rhaenyra or not, this caused tensions in the realm, with many in his court believing a queen should not take the Iron Throne.
7 Ser Criston's Admission
Rhaenyra and Alicent's feud over the years played a key role at the beginning of the Targaryen Civil War. When Alicent is digging into Rhaenyra's personal affairs, Ser Criston suddenly confesses to having an affair with the princess.
While there were many things that made the two of them not trust each other, Criston's confession to Alicent completely altered the way she viewed Rhaenyra. This not only led to Ser Criston being a key ally to Alicent but solidified the queen's inability to trust the princess.
6 Otto Replaced As Hand
One thing often misunderstood about Otto Hightower is that he was actually a good Hand to King Viserys and served him well. It was by serving the King well, and tactfully, that Otto often benefited in his own desires and vision for the realm.
It was shocking when Viserys chose to listen to Rhaenyra when she suggested he remove Otto as Hand of the King. After this, Otto adamantly told Alicent to not trust Rhaenyra and fight for her son's right to the throne. By removing the only family she had in the court, Rhaenyra made Alicent more guarded and, thus, more determined to place her children in a position of power.
5 Rhaenyra's Affair With Harwin Strong
One of Rhaenyra's biggest lies is the legitimacy of her three oldest sons. It's obvious why she protects the parentage of her father, claiming they are her Velaryon husband's children, because both themselves and she would be in danger had the truth ever surfaced.
Considering Rhaenyra couldn't have a romantic relationship with her husband, it was completely reasonable that she would seek comfort outside of her marriage, which was the couples' agreement when they got married. However, the obvious paternity of her children left her family vulnerable, making it easier for her enemies to use this affair to create doubt about her claim to the throne.
4 Aemond Loses His Eye
Aemond has some great quotes following his claiming of Vhagar. However, this triumphant moment for the young boy was bittersweet considering it resulted in the loss of his left eye. The hostility between Alicent and Rhaenyra has spilled over to their children at this point.
This was a turning point because, though the children hadn't been friendly up to this time, they had yet to get violent with each other. This event not only proved the Targaryen heirs were willing to shed blood within their own house, but it demonstrated how far Alicent's hatred had gone. Not only does Aemond lose an eye, but Alicent attempts to disfigure one of Rhaenyra's children as retribution.
3 Vaemond Challenges The Heirs
For much of the earlier episodes of the series, the plotting to legitimize Rhaenyra and her heirs was largely within the Targaryen house. However, when Vaemond Velaryon dares to accuse Rhaenyra's sons of being bastards, in front of the court and king, he makes an open mockery of the heir.
This event demonstrated that tensions were not only within the Targaryen family, and other lords were concerned about the claim Rhaenyra's bastard-born sons had. While they are still of Targaryen blood, Vaemond's bold display made a public display of the instability of the Targaryen house.
2 Viserys' Death
The heartbreaking death of Viserys brought an end to the time of peace within the realm. Though the king attempted to calm the tensions within his house, it was in vain and by his death, there were too many years of hatred and plotting within the Targaryen family.
The event of his death, due to his delirium shortly before, made Alicent mistakenly think he wanted Aegon to be king. Though he was actually talking about Aegon the Conquerer, the queen's misunderstanding would lead her and the council naming Aegon king, usurping the throne from the heir Viserys had adamantly supported throughout his reign.
1 Vhagar Kills Lucerys
If the Green Council's decision to usurp Rhaenyra's throne wasn't enough to begin a deadly war within the Targaryen house, the death of the queen's son was certainly a reason. In this scene, Aemond was clearly seeking to frighten the young boy, but his dragon became defensive after Arrax assaulted her, causing Vhagar to kill both dragon and prince.
The death of a Targaryen due to the fury and unpredictability of a dragon was an appropriate way to solidify Rhaenyra's decision to fight a war. Though she hesitated initially, especially with dragons in a battle that could cause such massive devastation, her reaction to hearing of her son's death demonstrated that in that moment, everything had changed.