Muhammad al-Nasir crosses the Strait of Gibraltar in 1209 with a powerful war machine, invading Christian territory and capturing the stronghold of the Calatrava Knights (now known as the Order of Salvatierra) in Salvatierra.

After this, the threat is so great for the Iberian Christian kingdoms that Pope Innocent III calls European knights to a crusade.

The Almohads had taken important cities as Trujillo, Plasencia, Talavera, Cuenca and Uclés after the defeating Alfonso VIII of Castile in 1195 in the so-called Disaster of Alarcos.

Muhammad An-Nâsir, who had succeeded his father, Abû Yûsuf Ya'qûb al-Mansûr, as Almohad caliph in 1198, has inherited an empire that is showing signs of instability.

Because of his father's victories against the Christians in al-Andalus), an-Nasir had been temporarily relieved from serious threats on that front and able to concentrate on combating and defeating attempts by the Banu Ghaniya to seize Ifriqiya (Tunisia).

Needing, after this, to deal with problems elsewhere in the empire, an-Nasir had appointed Abû Muhammad ben Abî Hafs as governor of Ifriqiya, thus unwittingly inaugurating the rule of the Hafsid dynasty here, which is to last until 1574.

He now has to turn his attention back to Iberia to deal with the crusade proclaimed by Pope Innocent III.

Alfonso VIII of Castile and Leon, immobilized since 1195 by his crushing defeat at Alarcos at the hands of the Almohads, gains the sympathy of the archbishop of Toledo, Rodrigo Jiménez de Rada, who proceeds to stir up religious indignation at the Muslim victory over Christians.

The proclamation of a crusade, obtained from Innocent, has elicited further support from several French bishops; and, in the spring of 1212, contingents of French knights under the archbishop Arnold of Narbonne and Knights Templars began to converge on Toledo.

After some delay, the crusade sets out southward on June 21, augmented by the armies of Alfonso’s Christian rivals Pedro II of Aragon and Afonso II of Portugal.

An early battle is the reconquest of Salvatierra, which is returned to its former masters.

The non-Spanish forces, despite their success in taking two Muslim fortresses, are soon discouraged by adverse climatic and living conditions and return home.

The armies of Navarre, however, are now recruited for the expedition.

The Almohad caliph Muhammad an-Nasir had meanwhile moved to Jaén on June 22, then …

…the mountainous area around Baeza, intending to cut off the Christians at the plain of Las Navas de Tolosa, about forty miles (sixty-four kilometers) north of Jaén.

An-Nasir’s army is composed of forces from the entire Almohad empire.

Most of the men in the Almohad army come from the African side of the empire, which includes Morocco, Algeria, Tunisia and even as far away as Mauritania and Senegal, in addition to much of the Iberian peninsula's southern half.

The Christians, soon after their arrival on July 12, take Castroferral with hopes of then reaching the Muslim encampment through the pass of La Llosa.

The pass is heavily guarded, however, and it is through a local shepherd who directs the Christians to an alternate opening that they are able to reach the Muslim base.

Alfonso himself leads the Christians into battle and shatters the Almohad forces on July 16 at the battle of Las Navas de Tolosa (also called the Battle of Al-Ôuqab).

An-Nasir flees, while …

…Alfonso follows up his victory by immediately taking Baeza and …

…Úbeda; the defeated Almohads retreat to their North African provinces, withdrawing entirely from Spain but continuing to rule in Morocco.