Union of the Crowns of Castile and León

Timeline

1. 1230Sahagún · LeónKing Alfonso IX of León died at Sahagún; his will left León to his daughters Sancha and Dulce, but Ferdinand III, as eldest son, claimed succession based on the earlier Treaty of Tordesillas. The León nobility was divided, and the succession dispute was on the verge of breaking out.
2. 1230City of León · LeónFerdinand III led his army into León and, with noble support and military pressure, established control over the Crown of León. His sisters Sancha and Dulce withdrew after receiving compensatory estates, averting a large-scale civil war, and both crowns came to rest in Ferdinand's person.
3. 1230–1231Burgos · BurgosFerdinand III convened cortes in Burgos and elsewhere, integrating the administrative, military, and ecclesiastical systems of Castile and León and unifying reconquest strategy. The union of the crowns created the largest Christian Iberian kingdom, directly driving southward expansion in the 1230s.