The Andals began in the tiny peninsula northwest of Qohor known as the Axe, but have expanded with startling swiftness to make Andalos into a prominent kingdom in northwest Essos, covering the Hills of Norvos and the fertile lands between them and the Narrow Sea. Andalos was bordered by the Rhoynar to the south (that border now in question), coastlines to the west and north, and the Forest of Qohor to the east, and most of the land ruled by these people is made up of hills and river valleys. This contrast of mountainous terrain cut by the flow of water throughout has given the Andals access to a fair amount of wealth in metal and gems as the cutting rivers expose veins of minerals throughout the hills, and with this wealth the Andals were able to acquire one thing that has aided in their rise to prominence: the secret of iron.
Rich in metals but initially poor in knowledge and skill, the Andals were at first merely seen as a religious faction. Emerging from the Axe with the stated intent of spreading their Faith of the Seven, the Andals moved at a slow pace in the initial expansion of their territory until the High Septon Norvo decreed that the Father and the Smith had appeared to him together, and directed him to treat with the Rhoynar for the knowledge of iron. Whether this story is true or apocryphal, it is a fact that the great city of Norvos was named for Septon Norvo, and it is true that during his term the Andals pooled much of their mineral wealth to convince the Prince of Groyan Drohe on the Upper Rhoyne to train some of their smiths in the working of iron. This marked a massive shift in the advancement of Andal culture, as the quality and durability of their tools and weapons both leapt forward by a century or more.
After the Dragonlords of Valyria arose and cast down the Empire of Ghis, they turned their eyes upon the rich lands of the Rhoyne, and when they went to war against the Rhoynar, the Andals could see that their home at the northern edge of that riverland was not secure for long. As such, they began forays to the west, and found a new land that was broad and full of possibility; and if it was already occupied by heathen lords who needed the light of the Seven brought to them, then all the better for their souls.
The Andals first landed in force in The Vale, and the fiercest battles they fight with the Bronze King are still in that kingdom to this day. Other sizeable forces, however, have also come ashore in The Stormlands, and from there they have been able to spread more easily, as the Storm King’s lands are less difficult to move through than the mountainous terrain of The Vale.