When the Moors took over the Peninsula in the 8th century, they ignored the Christians in the northern mountains since there was little wealth there; the Christian kingdoms that eventually developed out of the region would provide a staging ground for the reconquista. These nations and the rest of Christian Europe had strong ideological motivations to push for the reconquest; there was actually more crusading in the peninsula from countries like France etc. than there was in the East.

Also, there was no "moorish Kingdom" in this period, there was a civil war in the early 11th century that fractured the region into about three dozen feuding muslim city states. Plenty of the Muslim rulers had alliances with Christian kings against other Muslims and vice versa, there really wasn't as much of an "us vs. them" mentality as is often portrayed. Anyway, due to all the Muslim infighting and the religious motivations of the French etc, it wouldn't have been too hard to pick city-states off one by one until the Muslims were too weak to do anything.

Hope that helps!

As someone who is doing extensive research on the final years of al-Andalus, I can't really say much for the initial brunt of the Reconquista in the 1250s, but there are a few reasons why Granada fell in the 1490s, which was seen by contemporaries (and is still viewed today) as the final chapter of the Reconquista.

The first is that the Moors were plagued by civil wars during the 1480s between Muhammad XII and Muhammad XIII. In a move to unify the populace, the latter made the unfortunate choice of invading cities in the recently unified Castile and Aragon shortly after he usurped the throne. The forces of the former used the Spanish to weaken Muhammad XIII, and the Christians used the whole mess to their advantage.

In contrast, Ferdinand and Isabella were hugely successful in unifying most of the Christian lands which often conflicted with each other (a success in which the Spanish Inquisition played no small part). Muhammad XIII's invasion of Castillian cities further unified the Christians against the common enemy of the Muslims. (I should also note here that Christian-Muslim relations following the first wave of Reconquista were...complex).

Ironically enough, I doubt the Christians would have stood much of a chance against Granada in the 1470s, as the roles were reverse (Christian Iberia was stuck in a series of civil wars while Granada stood more or less united).

I don't know if this is quite what you're looking for, but I hope it helped gain insight into the second wave of Reconquista.

Can a moderator step in here and demand some evidence?

I am currently researching at the Archive of the Indies in Seville. some of these posts sounds right but I want sources.