The War of the Usurper
"War of the Usurper some call it, Some call it the war of justice for Orys Baratheon and some call it the war against the tyranny of House Targaryen, it does not matter however what it is called, the truth matters, Robert Baratheon sent out raven across the realm, asking the Lords to support his claim on the throne to root out the corrupted Targaryens and the realm bled, once again." - Lord Rodrik Stark after the War of the Usurper
It all started when King Aeryn demanded Lord Ronnel Tully to travel to King's Landing for striking down the Targaryen banners from his halls, instead of doing so he rose the banners of House Baratheon on his keep and his bannermen did so too, resulting in the King demanding Lord Tully's head, which led to the War of the Usurper.
Robert Baratheon called his banners, not to follow the king's demands, but instead starting a war to take the throne from the Targaryens , he called his allies, House Tully and the Riverlands were the first to join him against the tyranny of the targaryens. Soon followed by House Stark and the North due to their longterm relationship since Orys Baratheon. House Belmore and the Vale also called their banners and followed Robert Baratheon, as did House Lannister and the Westerlands.. And suprisingly House Chester and the Reach also rose up for Robert Baratheon, leaving King Aeryn with only the crownlands, the claw and the Stormlands at his side as Dorne stayed neutral.
The First Major Battle
The first major battle was fought near Highgarden between the crownlander troops led by the King himself against the Reachmen under Lord Chester and Lord Osgrey. They were eventaully defeated but not before a young knight that was eager to prove himself managed to kill the King's dragon, destroying most of the hope of King Aeryn to keep his throne.
Though their armies were mostly killed, Lord Chester and Lord Osgrey did not surrender their arms and continued to fight King Aeryn.
The Second Major Battle
The second major battle was fought in Dyre Den, One of the armies of the riverlands was sieging Dyre Den to eliminate the Claw from supporting the King, however the King himself tried to attack the riverlander army that was outnumbered.
The riverlander army was starting to lose hope as their lines started to collapse, until a fleet of Valemen arrived to save the riverlanders and together they destroyed the King's forces.
Third and Last Major Battle
The third and last major battle was near Oldtown where the stormlander armies tried to defend the Red Keep against the advancing forces of the rebelling houses, however their armies were split up and were crushed soon after, one of the armies was smashed by the Northern army, led by Rodrik Stark, while the other army was crushed by the combined forces of the Lannisters, Baratheons and Tullys.
Siege of the Red Keep
With the crown's forces destroyed there was one last thing to do, taking the Red Keep where King Aenys was hiding with his remaining forces.
House Osgrey had sieged the Red Keep for months and with the last of the crown's forces destroyed, they had enough men to lead an attack on the Red Keep itself, which fell within days of the assault.
After the war House Targaryen was knocked off the throne, the former King Aeryn demanded a trail by combat but it was denied and he was executed shortly after.
It is recorded by the maesters in the citadel that the King was constantly shouting traitors, yet he was completly silent when he heard the judgment of Robert Baratheon, he got the same trial he gave to Banfred Lannister, his own kingsguard member.. Which was none but a swift execution. It is said that Bertram Lannister, the brother of Banfred gave his first smile since the news of his brother's death when he saw Aeryn executed.
Aeryn's family was untouched by Robert Baratheon and was allowed to stay in Oldtown, but they left shortly after Robert's crowning.
House Targaryen of the Stormlands were only demanded to bend the knee, which they did.
The capital was moved from Oldtown to Hammerhorn.
The Bay of Claws was split between the Vale and Riverlands while the Claw itself was given to a cadet house of House Targaryen, House Blackfyre. The Northern Reach was granted to House Osgrey while House Chester was granted the Southern Reach, including the Red Keep itself.
Robert Baratheon was after the war crowned in Hammerhorn by the High Septon as King Robert Baratheon, First of his Name, King of the Andals, the Rhoynar and the First Men and Protector of the Realm.