At the height of its power in the 14th and 15th centuries, the Crown of Aragon was a thalassocracy a state with primarily maritime realms controlling a large portion of present-day eastern Spain, parts of what is now southern France, and a Mediterranean "empire" which included the Balearic Islands, Sicily, Corsica, Sardinia, Malta, Southern Italy from and parts of Greece until The component realms of the Crown were not united politically except at the level of the king, who ruled over each autonomous polity according to its own laws, raising funds under each tax structure, dealing separately with each Corts or Cortes.
Put in contemporary terms, it has sometimes been considered that the different lands of the Crown of Aragon mainly the Kingdom of Aragon, the Principality of Catalonia and the Kingdom of Valencia functioned more as a confederation than as a single kingdom. In this sense, the larger Crown of Aragon must not be confused with one of its constituent parts, the Kingdom of Aragon, from which it takes its name. In , a new dynastic familial union of the Crown of Aragon with the Crown of Castile by the Catholic Monarchs, joining what contemporaries referred to as "the Spains" led to what would become the Kingdom of Spain under King Philip II.
His long reignβthe longest of any Iberian monarchβsaw the expansion of the Crown of Aragon in three directions: Languedoc to the north, the Balearic Islands to the southeast, and Valencia to the south. By a treaty with Louis IX of France, he wrested the County of Barcelona from nominal French suzerainty and integrated it into his crown. He renounced northward expansion and taking back the once Catalan territories in Occitania and vassal counties loyal to the County of Barcelona, lands that were lost by his father Peter II of Aragon in the Battle of Muret during the Albigensian Crusade and annexed by the Kingdom of France, and then decided to turn south.
One of the main reasons for this formal renunciation of most of the once Catalan territories in Languedoc and Occitania and any expansion into them is the fact that he was raised by the Knights Templar crusaders, who had defeated his father fighting for the Pope alongside the French, so it was effectively forbidden for him to try to maintain the traditional influence of the Count of Barcelona that previously existed in Occitania and Languedoc.
As a legislator and organiser, he occupies a high place among the European kings. James compiled the Llibre del Consolat de Mar, which governed maritime trade and helped establish Aragonese supremacy in the western Mediterranean. He was an important figure in the development of the Catalan language, sponsoring Catalan literature and writing a quasi-autobiographical chronicle of his reign: the Llibre dels fets.
