After the union of Catalonia and Aragon by the marriage, then rule, of Queen Petronilla in 1137, the kingdom’s main phase of expansion came under James I, ‘the Conqueror’ (r. 1285–1327). He reconquered the Kingdom of Valencia and the Balearic Islands from the Moors, and annexed Bearn and Languedoc from France, although he renounced claims to Provence by the Treaty of Corbeil (1258). In 1282, Peter III of Aragon seized Sicily but, for the next century, Aragonese monarchs were bedevilled by the Union of Aragon, an alliance of the nobility that sought, often by force of arms, to preserve their independence from the Crown. Distracted, Aragon lost its trans-Pyrenean possessions and the Duchy of Athens. Their fortunes turned under Alfonso V, ‘the Magnanimous’ (r. 1416–58). In an eventful reign, he completed the conquest of Sardinia, recaptured Sicily, lost then restored his control of Naples, and gained control of the Adriatic through overlordship of Albania.
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