Yusuf ibn Tashfin came to al-Andalus from the Maghreb to help the Muslims fight against Alfonso VI of León, eventually achieving victory in Sagrajas and promoting an Islamic legal system in the region.

[12] The Sanhaja were linked by medieval Muslim genealogists with the Himyarite Kingdom through semi-mythical and mythical pre-Islamic kings and for some reason, some of the contemporary sources (e.g., ibn Arabi) add the nisba al-Himyari to Yusuf's name to indicate this legendary affiliation.

[15] This sort of trust and favor on the part of a seasoned veteran and savvy politician reflected the general esteem in which Yusuf was held, not to mention the power he attained as a military figure in his absence.

Daunted by Yusuf's new-found power, Abu Bakr saw any attempts at recapturing his post as politically unfeasible and returned to the fringes of the Sahara to settle the unrest of the southern frontier.

Yusuf was an effective general and strategist who put together a formidable Army comprising Sudanese contingents, Christian mercenaries and the Saharan tribes of the Gudala, Lamtuna and Masufa,[16] which enabled him to expand the empire, crossing the Atlas Mountains onto the plains of Morocco, reaching the Mediterranean Sea and capturing Fez in 1075, Tangier and Oujda in 1079, Tlemcen in 1080, and Ceuta in 1083, as well as Algiers, Ténès and Oran in 1082–83.

Previously, the emir had launched a series of aggressive attacks on neighboring kingdoms, so as to amass more territory for himself, but his military aspirations and capabilities paled in comparison to those of the Leonese king, who in the name of Christendom, in 1085, captured Toledo and exacted parias, or tribute, from Muslim princes in places such as Granada, al-Mu'tamid of Seville being no exception.

These are the circumstances that led to the Almoravid conquest and the famous quote, rebuffing his son, Rashid, who advised him not to call on Yusuf ibn Tashfin, where al-Mu'tamid said: I have no desire to be branded by my descendants as the man who delivered al-Andalus as prey to the infidels.

He came to al-Andalus with a force of 15,000 men, armed with javelins and daggers, most of his soldiers carrying two swords, shields, cuirass of the finest leather and animal hide, and accompanied by drummers for psychological effect.

On October 23, 1086, the Almoravid forces, accompanied by 10,000 Andalusian fighters from local Muslim provinces, decisively checked the Reconquista, significantly outnumbering and defeating the largest Christian army ever assembled up to that point.

He saw the lax behavior of the taifa kings, both spiritually and militarily, as a breach of Islamic law and principles, and left Africa with the express purpose of usurping the power of all the Muslim principalities, under the auspices of the Abbasid caliph of Baghdad, with whom he had shared correspondence, and under the slogan: The spreading of righteousness, the correction of injustice and the abolition of unlawful taxes.

In 1097, on his fourth trip to al-Andalus, Yusuf sought to personally dig down and fight the armies of Alfonso VI, making his way towards all but abandoned, yet historically important, Toledo.

After El Cid died in the same year, 1099, his wife Jimena began ruling until the coming of another Almoravid campaign at the tail end of 1100, led by Yusuf's trusted lieutenant Mazdali ibn Tilankan.

He was described as: A wise and shrewd man, neither too prompt in his determinations, nor too slow in carrying them into effectYusuf was very much adapted to the rugged terrain of the Sahara and had no interests in the pomp of the Andalusian courts.

Ali ibn Yusuf in 1135 exercised good stewardship by attending to the University of Al-Karaouine and ordering the extension of the mosque from 18 to 21 aisles, expanding the structure to more than 3,000 square meters.

Some accounts suggest that to carry out this work Ali ibn Yusuf hired two Andalusian architects, who also built the central aisle of the Great Mosque of Tlemcen, Algeria, in 1136.