What happened with the Muslim Majority of Spain?

Due to the lack of reliable contemporary sources, it's hard to know exactly what happened when the Muslims entered the Iberian Peninsula, or why. However, a combination of possibly authentic contemporary sources and later written accounts give us an idea of what occurred, starting with the prior Muslim conquest of Macreb and the ongoing Visigoth civil war in Hispania. While it's not crystal clear as to how the Visigoths in Hispania had turned on each other, it does seem evident that a civil war was afoot in the early 8th century. The Visigoth elites had been on a downward spiral for some time, and upon the death of their king, Vitissa, the situation escalated rapidly. There was no clear successor, as none appeared to have majority support, although two contenders stood out in particular, Roderick and Aquila II. Sources conflict when it comes to who was or if there was one single king at the time of Islam's entry into Spain, but it's generally believed that there was a state of royal division based on numismatic evidence. In this reality, Aquila would have ruled over the Ebro basin and Septimania, while Roderick managed the rest. It was Roderick, however, who proved most relevant in the events to follow. As the Visigoth kingdom of Hispania was struggling to stay afloat in 711, North African Umayyad governor Tariq ibn Ziyad led thousands of his Muslim warriors into southern Spain. King Roderick led his own men against the invaders, meeting them in the south at the Battle of Guadalete. Though there is a severe lacking of contemporary sources recounting the events of the invasion as a whole, we know that the Battle of Guadalete was decisive and brought about the death of the Visigoth king. How the monarch died is not entirely clear, but it's speculated that a portion of the Visigoth army refused to support the alleged usurper king, and thus either withdrew entirely or, at a minimum, pulled back enough to allow the Muslim attackers to surround the fighting portion of the Visigoth troops. The latter was then routed, and Roderick was slain in the final leg of the battle. Now, the door was wide open for Tariq and his men to push forward. The surviving Visigoths remained divided and at odds with each other, and the Muslims soon gained reinforcements under the command of Musa ibn Nasir. Aside from a small region on the northern border, the Umayyads had seized the whole of the Iberian Peninsula in only a few years. Their next challenge was to set up a new administration to manage what would now be named Al-Andalus. However, this was not altogether difficult for the Muslims to do. While religions and cultural differences between the invaders and their victims were stark, much of the Visigoth elite hadn't cared all that much about supporting their kingdom anyway, and thus would do whatever they were asked in order to protect their own power. This led to a series of agreements between the Umayyads and Visigoths which ultimately kept life fairly consistent for the conquerors' new Christian subjects. Many of the local Christians nevertheless would soon begin converting to Islam, though exact numbers are unknown, and Spain would remain under Muslim rule for centuries. From the Umayyad Caliphate to the Emirate of Granada, the Iberian Peninsula was becoming more and more Islamic. However, this was still a temporary status, because as we know, Spain would soon become synonymous with Christianity yet again. The Christian inhabitants of the region had been piece by piece chipping away at the Muslim rulers in Iberia in an effort known as Reconquista, starting back in the 8th to 9th century. In 1035, the Kingdom of Aragon was established on the east end of the peninsula by the Christian reconquerors, shortly followed by the formation of the Kingdom of Castile toward the center, which would eventually be sandwiched by the Christian Kingdom of Portugal. This left a relatively small chunk of Iberian lands to the Muslim conquerors, and internal strife was beginning to bubble with the remaining emirate. As the Muslim stronghold weakened, the Christian kingdoms were strengthening. In 1469, Ferdinand of Aragon and Isabella of Castile were wed, and the race was on to once and for all unite the Spanish lands. After convincing Pope Sixtus IV to deem the planned invasion a crusade, the Catholic monarchs, as they were often called, laid siege to the Muslim resistance. On January 2nd, 1492, the Sultan of the Emirate of Granada, Muhammad XII, finally surrendered his land to the Christian kingdoms, and just like that, Al-Andalus was no more. Nevertheless, the Islamic faith throughout Iberia didn't disappear overnight. At its peak, Islamic Spain had housed upwards of 5 million Muslims, and while the number had declined somewhat drastically by the fall of the Emirate of Granada, there were still at least half a million Muslims throughout the Al-Andalus lands. This is because at first, the Christian reconquerors had opted to feign tolerance for both the Muslim and Jewish populations within Iberia. In the Treaty of Granada, the Catholic monarchs agreed to treat their new Muslim subjects, or Moors, with tolerance and fair treatment. As for the Jewish citizens, the treaty gave them the option to either convert to Christianity or leave the Iberian Peninsula within the next three years. This agreement, however, never really mattered to the Spaniards. In March of 1492, Ferdinand and Isabella issued the Alhambra Decree, which ordered the full expulsion of all practicing Jews from all of the monarch's territories. Any who wished to remain in Spain would be required to convert to Catholicism, and many reluctantly did. There was also a push for the remaining Moors to convert to Catholicism alongside the Jews, notably urged by the Archbishop of Granada, Hernando del Talavera, and the Archbishop of Toledo, Francisco Cisneros. By 1499, pressure for such forced conversions sparked a rebellion among the Moors, but this only ended in the complete reversal of religious tolerance from the Catholic monarchs, who now gave the Muslims the same ultimatum that the Jews had previously received. This drastically reduced the Moor population throughout the Spanish lands, but it wouldn't be the last expulsion either. At the beginning of the 17th century, King Philip III of Spain issued a decree aimed at expelling all descendants of the former Muslim population, even those who had converted to Catholicism. By this point, the Arabic language had already been outlawed by Philip II, and Arabic books had been burned en masse. It's believed that the fear of continued rebellions and a want for religious unity is what led to these acts, but whatever the reason, they made being a Muslim in Spain essentially impossible. It's believed, formally, that indigenous Islam had finally come to an end in Spain by 1727, after the final large-scale crackdown on those who had remained. All the while, the Muslim world of North Africa and the newly expanded Ottoman Empire had become safe havens not just for Muslims, but even for the Iberian Jews. Many of both faiths had fled to these lands as opposed to trying to remain on the Iberian peninsula in the face of persecution. By this point, there wasn't much of a reason for any religious minority to remain under the Spanish crown, especially for the Jews and Muslims. This means that the answer to what happened to the Muslim majority in Spain can be explained in two parts. For one, the fall of the Muslim leadership over Al-Andalus meant that many Muslims began to leave or convert voluntarily as they saw their own rulers and final Islamic emirate collapsing around them. But given that there were still around half a million Muslims in the Spanish lands even at the time, it's clear that something else caused indigenous Islam to die out, and that's exactly the case. The Catholic monarchs and their descendants saw no reason to follow the rules they'd agreed to with the Treaty of Granada, and overall had essentially no tolerance for religious dissension. Thus, the determination to force conversions and expel all Jews and Muslims who refused to become Catholic led to a stunning decrease in both populations. As for the Muslims, the Spanish crown gave no leniency by the reign of Philip III even for the descendants of the converts to Christianity. This ensured that even Islam being practiced in secret would disappear from the kingdom, and with the nearby North African and Ottoman lands welcoming the expelled Muslims and their descendants with open arms, why would they have wanted to stay in Spain anyhow?