Hey guys! So first off this is my first story so please give me any feedback you can, I'm really excited to be writing this. I'd recommend you read this so you can have an understanding on how I explained away Northern Independence here. Hope you guys enjoy this!
The North is the only Kingdom that was never conquered by the Targaryens. This is due to a variety of reasons: First, after Joramun and Brandon the Breaker joined forces to defeat the Night's King (13th Lord Commander of the Night's Watch) Joramun decided to pledge the Free Folk to the Starks. This means that the Children of the Forest, Giants and Wargs are common throughout the North, not only Beyond the Wall. There were some problems of course, since the Free Folk are a proud people, but one by one clans saw the benefits of being allied to the Starks and bent the knee. Second, the North is a lot more populated here. They can raise about 160,000 fighting men. Third, they are as wealthy as the Westernlands. The North has lots of trade with Essos, specifically Bravos, and their mountains are rich in gold, silver and iron. Fourth, the North has established a Royal Army of 20,000, a Royal Navy of 10,000 and changed the purpose of the Night's Watch (which is used as a peacekeeping force only for the defense of the North, not what it is in cannon) which is manned by 10,000 Men. All of these answer directly to the Crown of Winter. Fifth, to invade the North by land you have to get through the Twins (House Frey was erased), the Neck and Moat Cailin (which is in perfect condition with all of its 20 towers functioning).
Aegon's Conquest proceeded in the same way, but after the Field of Fire instead of turning North they decided to consolidate their power. This was due to the fact that the North could raise more fighting men than the other kingdoms and its long history of defending against Andal invasions. With 5 of the 7 Kingdoms and the Iron Islands under their control they decided that would first try to conquer Dorne and have all of the South under the Dragon's banner before turning North, since a Northern Campaign would undoubtedly be a lot harder. Rhaenys, sister-wife to Aegon, eventually died in the Dornish Marches and all plans of a Northern Conquest were put on hold.
War of 73 AC:
In 73 AC Jaehaerys the Conciliator made the decision to commence a Northern Conquest, where they gathered 100,000 men to attack the North, led by Prince Aemon, Jaehaerys' heir, and Baelon Targaryen, the heir to the heir. They lost 10,000 men taking the Twins and 5,000 more while marching through the Neck. Once they got to Moat Cailin, they were met by 80,000 men and 2,000 Armored Giants led by King Alaric Stark. The Giants were armed with huge bows which could theoretically shoot down Dragons. This made the Targaryens cautious, and they didn't use their dragons for the first 3 days, instead testing Moat Cailin's defenses. They lost 25,000 men before they decided to use their dragons on the 4th day of battle. This proved to be a mistake, as they shot down Prince Aemon's mount Caraxes, resulting in his death from the fall. Enraged by his brother's death and that of Caraxes, Baelon Targaryen ordered an all out attack on the 5th day of battle, where another 20,000 Targaryen men were killed by the Northmen and Giants. Prince Balon's mount, Vhagar was killed as well but he managed to survive the fall. He was subsequently captured, which caused the remaining 20,000 men surrendered and word was sent out to King Jaehaerys and Queen Alysanne, who quickly flew North to discuss terms. Threatened by Ironborn raiding the Westernlands and the Reach, they had no other choice but to sue for peace. The Iron Throne paid 2 Million Gold Dragons to the North in reparations and left with Baelon, the new Heir to the Iron Throne. This came to be known as "The Northern Massacre". Only 20,000 Northmen and 400 Giants died, while the Targaryen army suffered 60,000 casualties, while also losing 2 Dragons and the heir to the Iron Throne. This campaign permanently ensured Northern Independence.
In 280 AC King Rickard Stark visited King's Landing to discuss trade deals between the North and the Iron Throne. He had never visited the city, and in his curiosity he decided to go personally to these negotiations. Aerys had him killed almost immediately after he visited the city and then declared war on the North. In response, Brandon Stark, newly crowned King in the North, gathered 80,000 men to march South. The Westernlands, Stormlands, Vale and Riverlands refused to take part in the war. The Dornish were forced to march due to Elia being a hostage to Aerys and the Reach lords were eager for glory, hoping that they could finally stamp down the Old Gods. Aerys declared all those who refused to fight in the war rebels and declared war on them too. The Vale, Riverlands and Stormlands banded together while Tywin bided his time. The Rebel Coalition declared Robert King and with the help of the Northmen they made quick work of the Loyalist Army. Lysa Tully married Jon Arryn and Catelyn Tully married Ned Stark, while Cersei Lannister married Robert Baratheon after the Lannister sack of King's Landing.
Stark Cadet Branches:
1. House Moatstark- Rulers Moat Cailin, and were descended from a brother of a Theon Stark, the hungry wolf, who had warned by greenseers of future Andal invasions by land after his campaign in Andalos.
2. Goldstarks- They rule the Mountain Clans. They are on of the richest houses in the North, courtesy of their Gold Mines.
3. Seastarks- Rulers of the Stony Shore, the first line of defense against Iron Born attacks.
4. Skagstark- Rulers of Skagos ever since Skagosi lords rebelled against the crown. It was passed onto Stark hands after the fact. House Skagstark are rich off of trade due to their closeness to Essos.
5. Karstark- Cannon house guys, look it up in the wiki if you have too :)
6. Northstark- Rulers of Hardhome, another trade city.
7. Snowstark- Rulers of Queens Crown.
8. Winterstark- Rulers of the Gift.
9. Ironstark- Based in the Flint Cliffs.