This is latest chapter in Norman Davies‘ Vanished Kingdoms, about forgotten states in Europe. Aragon is at least somewhat more familiar from the Christopher Columbus tale. Its origins go back for centuries before that.
When the Moslems conquered Spain and drove on into France, most if not all of the original political rules were tossed aside. Turned back at the battle of Tours, the Moslem tide receded and was pushed back. By the time of Charlemagne in 800 AD, they had been pushed over the Pyrenees Under lesser rulers this could not be sustained, and soon the mountain region gained its independence from both states and several tiny mountain states formed in this contested region.
With time Moslem power continued to wane and these border states expanded south. Aragon did as well, and then unified with the County of Barcelona to reach the coast. It basically covered current Catalonia, plus a smidgen of France north of the mountains.
Squeezed out of facing the Moslems, expansion began overseas. First the Balearic Islands were taken, then Corsica, Sardinia, Sicily, Malta, Southern Italy and parts of Greece were taken into this naval empire. But by the 1450s, attention began to shift to Spanish unification and then to the New World, and the island empire began to fall away. This got even worse as the Hapsburgs took over Spain and most of Europe and in the reaction other nations began to detach these parts, and Aragon descended into just another province in Spain. Even when resentment led to revolts, it was called Catalan rather than Aragonese.