Yusuf I of Granada

Coming to the throne at the age of fifteen, he was initially treated as a minor and according to Ibn al-Khatib, his authority was limited to only "choosing the food to eat from his table".[6] His grandmother, Fatima and the vizier Abu Nu'aym became his tutors and exercised some powers of government, together with other ministers. Upon his accession he took the laqab (honorific or regnal name) al-Mu'ayyad billah ("He who is aided by God"). The practice of taking a laqab was done by the founder of the dynasty Muhammad I of Granada (whose laqab was al-Ghalib billah, "Victor by the grace of God") but not by subsequent sultans before Yusuf, but after Yusuf this was done by almost all the sultans.[2] According to the Christian chronicles, Yusuf immediately requested to be under the protection of Abu al-Hasan Ali of the Marinid Sultanate, his late brother's ally.[7]

The peace that Muhammad IV secured after the siege of Gibraltar was, by principles of the time, rendered void by his death, and representatives of Yusuf I met with those of Alfonso XI of Castile and .[2][8] They signed a treaty at Fez, Morocco on 26 February 1334 with a four year duration. Like previous treaties, it authorised free trade between the three kingdoms, but unusually, it does not include payments of tribute from Granada to Castile. Marinid ships were to be given access to Castilian ports, and the Marinid Sultan Abu al-Hasan promised not to increase his garrison on the Iberian peninsula—but he could still rotate them.[9] The latter condition was favourable not only to Castile but also to Granada as it was also wary of the possible expansionism by the larger Marinid Sultanate in the peninsula.[2] Additionally, Alfonso IV of Aragon agreed to join the treaty in May 1334, and signed his own treaty with Yusuf I on 3 June 1335. After Alfonso IV's death in January 1336, his son Peter IV renewed the treaty for five years, therefore ushering a period of peace between Granada and all its neighbours.[10]

With the truce, the monarchs redirected their attentions elsewhere: Alfonso XI cracked down on his rebellions nobles, while Abu al-Hasan waged war against the Zayyanid Kingdom of Tlemcen in North Africa.[10] During these years, Yusuf I acted against the Banu Abi al-Ula family, the mastermind of Muhammad IV's assassination and the leader of the Volunteers of the Faith, the North African corps fighting in the Iberian Peninsula on behalf of Granada. In September 1340 (or 1338), Abu Thabit ibn Uthman, a prominent member of the family and one of the instigators of the assassinations, was removed from his post as the overall Chief of the Volunteers and replaced by Yahya ibn Umar of the Banu Rahhu family. Abu Thabit, along with his three brothers and the entire family was expulsed to the Hafsid Kingdom of Tunis.[2][11] Historian L. P. Harvey comments that "[b]y the standards of acts of revenge in those days ... this was quite restrained", likely because Yusuf did not want to unnecessarily cause enmity from the North African volunteers.[11]

On the spring of 1339, hostilities resumed with Marinid raids into the Castilian countryside. Various confrontations ensued between Castile on one side and the two Muslim kingdoms on the others. Granada was invaded by Castilian troops led by Master Gonzalo Martínez of Alcántara, who raided Locubín, Alcalá de Benzaide, Priego. In turn, Yusuf led his troops of 8,000 in besieging Siles but was forced to lift it by the forces of the Master of Santiago, Alfonso Méndez de Guzmán.[12] The personal rivalry between Gonzalo Martínez and Alfonso Méndez de Guzman appeared to have caused former to defect to Yusuf I, but he was soon captured by the royal forces, hung as a traitor and his body burned. The Marinid commander on the peninsula, Abu Malik Abd al-Wahid, son of Abu al-Hasan, died during a battle with Castile on 20 October 1339, but Marinid forces continued to ravage the Castilian frontiers until they were defeated in Jerez.[13]

On the fall of 1339, the Aragonese fleet under Jofre Gillabert tried to land near Algeciras but was driven away after the admiral was killed by the defenders' arrow.[14] On 8 April 1340, a major battle took place between the Castilian fleet under Alfonso Jofré Tenorio and a larger Marinid-Granadan fleet, resulting in a complete Muslim victory and the death of Jofré Tenorio. The Muslim fleet captured 28 galleys out of 44 in the Castilian fleet, and 7 carracks. Abu al-Hasan saw the naval victory as a harbinger for his conquest of Castile.[15] He crossed the Strait with his forces and siege engines, along with his wives and his entire court. He landed in Algeciras on 4 August, joined by Yusuf I laid siege on Tarifa, a port on the strait, on 23 September.[16] Alfonso XI marched to relieve Tarifa, joined by Portuguese troops led by his ally, King Afonso IV.[17] They arrived five miles from Tarifa on 29 October, and Yusuf and Abu al-Hasan moved to meet them.[18] Alfonso XI commanded 8,000 horsemen, 12,000 foot soldiers and unknown numbers of urban militia, while Afonso IV had 1,000 men.[17] The Muslim strength was unclear: contemporary Christian sources claimed an exaggerated 53,000 horsemen and 600,000 foot soldiers,[19] while Ambrosio Huici Miranda in 1956 estimated 7,000 Granadan troops and 60,000 Moroccans. Crucially, the Christian knights had much better armor than the Muslim light cavalry.[17]

The Battle of Río Salado, where Yusuf I and his ally Abu al-Hasan was defeated by the Castilian and Portuguese forces, in a 17th-century painting

The resulting Battle of Río Salado, on 30 October 1340, was a decisive Christian victory. Yusuf I, who wore a golden helmet in the battle, fled the field after a charge by the Portuguese troops. The Granadan contingent initially defended itself and was about to defeat Afonso IV in a counter attack, but was routed when enemy reinforcement arrived, leaving their Marinids allies behind. The Marinids too were routed in the main battle, which lasted from between 9 a.m. and noon.[20] Harvey opined that the key to the Christian victory—despite their numeric disadvantage—appeared to their cavalry tactics and superior armor. Muslims tactics—which focused on lightly armored, highly mobile cavalry was well suited for open field battle, but in the relatively narrow battlefield on that day, the Christian formation of armored knights attacking in well-formed battle line held the decisive advantage.[17] In the aftermath of the battle, the Christian troops pillaged the Muslim camp and massacred the defenceless women and children, including Abu al-Hasan's Queen Fatima, the daughter of the King Abu Bakr II of Tunis—to the dismay of their commanders who preferred to see her ransomed.[20] Numerous royalties and nobles were captured including Abu al-Hasan's son Abu Umar Tashufin. Among the Granadan dead was the father of the future vizier of Yusuf I and historian Ibn al-Khatib. Yusuf retreated to Granada through Marbella. Abu al-Hasan marched to Gibraltar, sent news of victory back home to prevent any rebellion in his absence, and crossed the strait to Ceuta on that very night.[21]

Various Muslim authors laid the blame on the Marinid Sultan, with Umar II of Tlemcen saying that he "humiliated the head of Islam and filled the idolaters with joy",[20] and Al-Maqqari commented that he allowed his army to be "scattered like dust before the wind".[21] Yusuf I appeared to not have been blamed, and continued to be popular in Granada.[11] Alfonso XI returned to Seville victoriously and paraded the Muslim captives as well as the booty taken by his army.[22] There was so much gold and silver that prices in as far as Paris and Avignon fell by one sixth.[23]

With the bulk of the Marinids retreating to North Africa, enabling Alfonso XI to act freely against Granada. He captured Alcalá de Benzaide, Locubín, Priego, and Benamejí.[24] The Castilian army ravaged the surrounding countryside, not only taking food but also destroying vines—causing lasting damage to the local agriculture without any benefit to the attackers.[25] During the siege of Alcalá de Benzaide, a major fortress thirty miles from Granada, Yusuf I moved to a strong position in Pinos Puente to block Castilian attempts to raid further into the rich plains surrounding the city of Granada. Alfonso XI extended the raids into more area to tempt Yusuf I to leave his position, but the Granadan army held its ground as the Castilians devastated the area surrounding Locubín and Illora.[25] As the siege progressed, Yusuf received Marinid reinforcement from Algeciras and moved ten kilometers ahead to Moclín. Again Alfonso was not willing to risk a frontal attack but unsuccesfully tried to provoke Yusuf into an ambush.[26] With relief unlikely, the Muslim defenders of Alcalá offered to surrender the fortress in exchange for safe conduct, to which Alfonso agreed; the capitulation took place on 20 August 1341. Yusuf then offered a truce, but Alfonso asked that he must break his alliance with the Marinids. Yusuf rejected, and the war continued.[27][2]