The Visigothic Kingdom was the state that dominated the Iberian peninsula. Firmly established by the 6th century AD, the Visigoths maintained their hold on Iberia tenaciously, though by the late 7th century, some of the northern provinces had drifted out of their orbit. Various insanguinary wars against the Franks resulted in only the independence of Septimania, which did far better against the Franks than the Visigoths.
Unification of the Peninsula
After the fall of the Western Roman empire, the Visigoths held the bulk of the peninsula and much of France too; until the Franks defeated the Visigoths in France, reducing them to Septimania - a little Occitan province centred around the port of Narbonne. In spite of these defeats, the Visigoths achieved far better than this, destroying the Suevi kingdom of Galicia and uniting the Iberian peninsula under one ruler.
Wars with the Franks
Seeing as there was little threat from the East - the Byzantine province of North Africa being under a very loose government and the Berber Kingdom of Mauretania not having either the required land or sea power to launch an attack across the Straits of Gibraltar - the Visigoths had a stab at regaining their provinces in France. It was hardly a major success; the Franks were more than capable of defeating the Visigoths at most major battles - and the only gains that were made in the entire war were made by Septimania, which declared its independence in response to the Visigothic monarchy's obvious incompetence.
Stagnation and Decline
The Visigoths, with their warlike nature, were unable to find anyway of venting their military desires. The border with the Franks to the north was closed, and the Berber Kingdom of Mauretania, while incapable of launching an assault against Iberia, were more than capable of defending their own territory from a naval assault by the Visigoths. They only saw combat when the occasional Viking raid landed, although the Vikings soon gave them up as the Visigoths were far too successful in beating them back. Gradually more and more Visigothic kings, unable to please their restless population, were forced to abdicate prematurely and slowly the country disintegrated. Eventually, in 968, it did split apart into three separate kingdoms, Galicia, Goth-Iberia and Andaulacia. The Franks had no trouble in taking over these divided kingdoms between 1035 and 1060. Each was turned into a Frankish March with a Marcher Lord appointed to rule over it. Gradually, the Franks started to migrate into this new territory, mixing blood with the Visigothic inhabitants.