King Alfonso VI is able to gain the allegiance from the kings of Castile, Galicia and Navarra and the count of Barcelona by political marriages and treaties.
With this new military power from an unified Christian state, he is able to claim the title of Imperator Totius Hispaniae (Emperor of all Hispania) for real, and is later acknowledged by the Pope as such.
With the new religious and military power, Alfonso is able to march on the Taifa kingdoms of Toledo and Zaragoza, dealing a fatal blow to Al-Andalus. Eventually, a Empire of Hispania is established.
Differences from OTL
A secularised and very Jewish and Christian-influenced form of Islam is very common in parts of Spain.
Judaism and Islam still have strong presence in Spain and have had historically.
The Spanish Inquisition never happened; Hispanidad is one of the most religiously-diverse places in the world.
The Rennaisance and the discovery of the Americas happened much earlier due to the riches of the Muslim World now avaliable to the west.