On 19 December 1308, at Alcalá de Henares, King Ferdinand IV of Castile and the ambassadors from the Crown of Aragon, Bernat de Sarrià and Gonzalo García agreed to the terms of the Treaty of Alcalá de Henares. Ferdinand IV, supported by his brother, Pedro de Castilla y Molina, the archbishop of Toledo, the bishop of Zamora, and Diego López V de Haro agreed to wage war against the Emirate of Granada by 24 June 1309 which was also when a previous peace treaty between Granada and Castile was set to expire. It was further agreed that the Aragonese monarch, James II, could not sign a separate peace accord with the Emir of Granada. A combined Aragonese-Castilian navy was also formed to support the siege in a blockade of the coastal Granadian towns. It was also stipulated that the Crown of Castile would attack the towns of Algeciras and Gibraltar and that the Aragonese forces would attempt to conquer the city of Almería.
Ferdinand IV promised to cede one sixth of the conquered Granadan territory to the Aragonese crown and therefore chose the entirety of the Kingdom of Almeria as its limits for the agreement with the exception of the towns of Bedmar, Alcaudete, Quesada, Arenas, and Locubin which would stay as part of Castile, having all previously been part of the Kingdom of Castile and León prior to their Muslim takeovers. Ferdinand IV further stipulated that if the lands taken from the Kingdom of Almería did not amount to one sixth of Granadan territory, that the Archbishop of Toledo would step in to resolve any differences related to the matter. These concessions to the Crown of Aragon led a few of Ferdinand IV's vassals to protest the ratification of the treaty, amongst them were John of Castile and Juan Manuel, Prince of Villena.
The concessions to Aragon, which had begun a period of relative irrelevancy compared to Castile, would once again restore the kingdom's power within the Iberian Peninsula. Aragon had previously reached its height under the Treaty of Cazola and the Treaty of Almizra which saw its territory and influence expand considerably. Ferdinand insisted on the Aragonese alliance to cement an alliance between Aragon and the Marinid dynasty so that they would not intervene in the coming war with Granada.
After the signing of the treaty at Alcalá de Henares, Castile and Aragon both sent emissaries to the court at Avignon to gain the support of Pope Clement V and to obtain the clerical backing of an official Crusade to further support military operations. They also asked for the papal blessing of a marriage between the Infanta Eleanor of Castile, the firstborn daughter of Ferdinand IV and Jaime de Aragón y Anjou, son and heir of James II of Aragon. The Pope agreed to both ventures and on 24 April 1309, Clement V issued the papal bull Indesinentis cure which authorised a general crusade against Granada to conquer the Iberian Peninsula together with mandates to conquer Corsica and Sardinia.
At the Courts of Madrid of 1309, the first courts to ever occur in the actual Spanish capital, Ferdinand IV publicly announced his desire to wage war against the Emirate of Granada and demanded subsidies to begin battle manoeuvres.