From A Wiki of Ice and Fire
The Andals are one of the three major ethnic groups of Westeros. Their arrival caused the fall of many of the kingdoms of the First Men which had developed in the wake of the Pact with the children of the forest. The Andals also brought the Faith of the Seven to the Seven Kingdoms.
The Andals are said to have originated in the Axe of northern Essos and then migrated and established Andalos in northwestern Essos, stretching south as far as the Flatlands and the Velvet Hills and engaging in conflict the with tribes that inhabited those lands, such as the so-called "Hairy men". Legend tells that they were visited by the incarnations of the Seven, who crowned their first king, Hugor of the Hill. They learned the art of working iron from the Rhoynar who lived along the Rhoyne.
It is unknown when the Andals sailed west across the narrow sea from Andalos to Westeros, some sources date the Andal invasion to six thousand years ago. According to the True History, it occurred four thousand years ago, but some maesters claim it was only two thousand years ago.
The Andals first landed in the Fingers and attacked the First Men living in the Vale. The original Andal invaders painted and carved the seven-pointed star of the Seven on their bodies.  They burnt out the weirwood groves, hacked down the faces and slaughtered the children of the forest that they came across. Everywhere they proclaimed the the triumph of the Seven over the old gods. A hill, now known to the Westerosi as High Heart, was sacred to the children of the forest. There, the Andal king Erreg the Kinslayer cut down the children’s grove of thirty-one weirwoods. It is said that the First Men killed half of the children of the forest with bronze blades, and the Andals finished the job with iron.
After several hundred years of war, the Andals conquered the six southern kingdoms of the First Men and created their own. Only the Kings of Winter resisted the Andals successfully, stopping them at Moat Cailin.  According to legend, at some point in time at the Nightfort, the Rat Cook served an unnamed Andal king a pie that was made of bacon and, unknown to the king, the king's own son.
Andal culture is marked by the strong influences it has had on the culture of the Seven Kingdoms. The Andals brought the Faith of the Seven to Westeros and with it the warrior tradition of the knight. The Andals used iron, while the First Men used bronze. The Andals also brought a superior writing system that supplanted the First Men's runes.
References and Notes
- ↑ The World of Ice and Fire, The Arrival of the Andals.
- ↑ 2.0 2.1 A Dance with Dragons, Chapter 5, Tyrion.
- ↑ A Game of Thrones RPG and Resource Book, Guardians of Order
- ↑ A Dance with Dragons, Chapter 48, Jaime.
- ↑ A Game of Thrones, Chapter 66, Bran, p 739.
- ↑ A Storm of Swords, Chapter 22, Arya, p 249.
- ↑ A Dance with Dragons, Chapter 33, Tyrion, p 373.
- ↑ A Game of Thrones, Chapter 66, Bran.
- ↑ A Feast for Crows, Chapter 5, Samwell.
- ↑ A Feast for Crows, Chapter 4, Brienne.