Robert's Rebellion

Robert's Rebellion, also known as the War of the Usurper, was one of the last great civil wars among the Great Houses of Westeros that took place approximately seventeen years before Game of Thrones begins, and lasted about one year; two, if one counts the Assault on Dragonstone as the final engagement of the conflict. It began just after the execution of Rickard Stark, head of House Stark, and his son and heir Brandon by the Mad King, Aerys II. The end of the war saw the collapse of the Targaryen dynasty with the deaths of the Mad King and his son and heir, Prince Rhaegar, and the ascension of Robert Baratheon to the Iron Throne, thus beginning the Baratheon dynasty. Despite this, the Mad King's two other children were safely smuggled across the Narrow Sea to Essos: Viserys and Daenerys Targaryen. Meanwhile, unknown to almost everybody, a grandson, Jon Snow, who is the son of Rhaegar and Lyanna Stark, is raised by his maternal uncle, Eddard Stark, who passes Jon off as his bastard son.

Background
Aerys II Targaryen, was King of the Andals and the First Men and the last member of House Targaryen to sit on the Iron Throne. The King is nicknamed the Mad King because his reign became increasingly erratic and murderous. Consequently, tensions between House Targaryen and several other Great Houses began to rise. The brutal fallout from Prince Rhaegar's alleged abduction of Lyanna Stark of Winterfell saw many noble houses in the realm rebel against his rule.

Lyanna was the daughter of Rickard Stark, Warden of the North, and betrothed to Robert Baratheon, the Lord Paramount of the Stormlands. House Stark and House Baratheon were the first to protest Rhaegar's actions. Brandon Stark demanded justice from Aerys in person. Aerys had him arrested for treason and then offered to ransom him to his father Rickard. Aerys summoned Rickard to court and, when he arrived, publicly and very brutally executed both father and son. The brutal murder of Brandon and Rickard engendered much sympathy for the rebels and many houses joined their cause.

Jon Arryn was the Lord Paramount of the Vale, the Warden of the East and a respected nobleman. Both Rickard's second son Eddard Stark and Robert were fostered with him as children and became close friends. When Aerys demanded that Eddard and Robert be turned over to the King's Justice, Lord Jon refused and raised his banners in revolt. The rebels forged an alliance with House Tully through marriage, with Eddard married to Catelyn Tully and the then-middle-aged Jon to the young Lysa Tully.

Stannis Baratheon fought for his elder brother Robert during the war. Aerys used his allies in House Tyrell to besiege Stannis at Storm's End for much of the war. Stannis's force was rescued from starvation by the smuggler Davos, who brought a ship full of onions and fish into the castle.

Rhaegar was killed during the fighting at the Battle of the Trident, slain by Robert himself. The site of his death is now called the Ruby Ford because it is believed to be scattered with rubies from his armor.

Rhaegar's wife Elia of House Martell was kept in King's Landing by Aerys to ensure the Martell's loyalty during the conflict. Aerys was betrayed by his allies in House Lannister. He was slain by his Kingsguard Ser Jaime Lannister. His final words were "Burn them all." The gates of King's Landing were opened to the Lannister armies and they sacked the city. Elia was raped and murdered by Ser Gregor Clegane during the Sack of King's Landing. Both of her children were also killed.

Robert claimed the Iron Throne because he started the war and killed Prince Rhaegar personally. Robert was also the only rebel leader to have a blood link to the Targaryens, as his mother had Targaryen blood. The other leaders of the rebellion refused the throne. Robert was devastated by Lyanna's death, but married Cersei Lannister as a show of gratitude to her father joining his cause late in the conflict and delivering the capital of King's Landing to him. Tywin remained the Lord Paramount of the Westerlands. Robert named Jon Arryn as his Hand while Eddard took his father's role as Warden of the North. House Tyrell, House Martell and House Greyjoy swore fealty to Robert to retain their pre-war positions, maintaining the Seven Kingdoms under their new royal house.

Queen Rhaella fled to the Targaryen's ancestral seat on the island of Dragonstone. She was accompanied by her son Viserys Targaryen, and was pregnant. Rhaella died soon after giving birth to Daenerys Targaryen. The children were taken into exile in the Free Cities by loyal retainers. Stannis went on to conquer Dragonstone and was made Lord of Dragonstone.

Unknown to most, after the Showdown at the Tower of Joy, Eddard found out that Rhaegar had another child, Jon Snow, by his sister, Lyanna Stark. Eddard raised the child as his bastard son to keep him safe Robert since he would have surely killed Jon if he found out about his true parentage.

In the books
In the A Song of Ice and Fire novels, this civil war took place between sixteen and fourteen years before the beginning of the novels. In the books the conflict is also called the War of the Usurper by Targaryen loyalists.

The war was sparked when Prince Rhaegar Targaryen kidnapped Lyanna Stark. When Lyanna's father and eldest brother protested this act to King Aerys II Targaryen, the Mad King had them both killed in front of the entire Royal Court. Aerys then called for the heads of Lyanna's betrothed, Robert Baratheon, and her second brother Eddard Stark, who were under the care of Jon Arryn. Lord Arryn raised his banners in rebellion against these unjust acts and sent Robert and Eddard back to their lands to rally their men.

House Tully joined Robert's side after Eddard and Jon married Catelyn and Lysa Tully, respectively, while House Tyrell and House Martell supported the Targaryens. While House Tully did support Robert, the always fractious lords of the Riverlands were heavily divided in the war, and many stayed loyal to the Targaryens. House Lannister sat out most of the war, only entering - on Robert's side - after Robert killed Rhaegar at the Battle of the Trident and his victory was a foregone conclusion.

The rebellion climaxed with the Battle of the Trident, when the rebel armies destroyed the royalist host and killed Prince Rhaegar. Lannister forces, apparently having decided to support the king, arrived at King's Landing to help defend the capital, but then turned on the Targaryens, brutally sacking the city and killing King Aerys II and Rhaegar's children. Aerys's other heirs, Viserys and Daenerys Targaryen, were spirited to safety across the sea by Targaryen loyalists before the garrison of Dragonstone (where the two children were being kept for their safety) could hand them over to Robert Baratheon. House Tyrell, whose main force had been held up in a lengthy siege at Storm's End, proclaimed loyalty to Robert soon after the sacking of King's Landing when Eddard Stark arrived with an army to relieve the siege.

In the aftermath of the war it was discovered that Lyanna Stark had died, so Robert married Cersei Lannister in thanks for her father delivering him victory and to secure an alliance between the two houses.

Elia Martell's brutal murder by the Lannisters during the Sack of King's Landing earned them the lasting enmity of the Martells. As a result of Elia's unnecessary and easily avoidable murder, Dorne became a hotbed of pro-Targaryen sentiment and it took lengthy negotiations on the part of Jon Arryn for them to grudgingly swear fealty to Robert.

Similar to the Lannisters, House Greyjoy remained neutral throughout most of the war, under the rule of Balon Greyjoy's father Lord Quellon. He had been a strong ruler though by the rebellion his health was failing. Quellon was not particularly loyal to either side, so he simply wanted the ironborn to wait out the war on the mainland. After Rhaegar died, however, his sons convinced him that they should side with the rebels while they still could, both to get a share of the plunder and to placate Robert Baratheon, soon to be the new king. They were not yet sure if Tywin Lannister would side with the Targaryens, so most of the Iron Fleet stayed home to defend against possible attack from the Westerlands. Quellon himself led a raiding fleet of 50 ships to attack the west coast of the Reach. They raided some soft targets, weakly defended villages and towns, but the Reach's main army was focused to the east at Storm's End. At the mouth of the Mander, however, the ironborn were attacked by a dozen Reach ships from the Shield Islands. They defeated them but lost a dozen of their own ships in the exchange, and Quellon died in the fighting. Balon then returned the fleet home. Overall it was a minimal, token gesture meant to please Robert, with absolutely no significant impact on the war. Characters in the main narrative of the novels have never even mentioned the Greyjoys' minimal activities in the war (Quellon's raiding is only known of through the World of Ice and Fire sourcebook). The Greyjoys had no deep allegiance to Robert, however, and a few years later Balon attempted to declare independence from the mainland in the Greyjoy Rebellion.