"Persecution of Jews was just that, while what happened with the Arabs was part of a conflict. There is no basis for comparison." — Jose Ribeiro e Castro, Portuguese lawmaker who drafted Portuguese law of return.

"Is Spain aware of what might be assumed when it makes peace with some but not with others? Is Spain aware of what this decision [not to include Muslims in the return] could cost?... Does Spain have alternatives to the foreign investment from Muslims?" — Ahmed Bensalh, Morisco-Moroccan journalist.

Observers say that by granting citizenship to all descendants of expelled Muslims, Spain, virtually overnight, would end up with the largest Muslim population in the European Union.

Muslim groups are demanding Spanish citizenship for potentially millions of descendants of Muslims who were expelled from Spain during the Middle Ages.

The growing clamor for "historical justice" comes after the recent approval of a law that would grant Spanish citizenship to descendants of Sephardic Jews expelled from Spain in 1492.

Muslim supporters say they are entitled to the same rights and privileges as Jews because both groups were expelled from Spain under similar historical circumstances.

But historians point out that the Jewish presence in Spain predates the arrival of Christianity in the country and that their expulsion was a matter of bigotry. By contrast, the Muslims in Spain were colonial occupiers who called the territory Al-Andalus and imposed Arabic as the official language. Historians say their expulsion was a matter of decolonization.

"Expulsion of the Moriscos at the port of Dénia", by Vincente Mostre.

In any event, the descendants of Muslims expelled from Spain are believed to number in the millions—possibly tens of millions—and most of them now live in North Africa. Observers say that by granting citizenship to all of them, Spain, virtually overnight, would end up with the largest Muslim population in the European Union.

Much of the Iberian Peninsula was occupied by Muslim conquerors known as the Moors from 711 until 1492, when the Moorish Kingdom of Granada surrendered to the Catholic Monarchs of Spain (Isabella I of Castile and Ferdinand II of Aragon), in what is known as the Christian Reconquest.

But the final Muslim expulsion from Granada did not take place until over a century later, beginning in 1609, when King Philip III decreed the expulsion of the Moriscos.

The Moriscos—Moors who decided to convert to Catholicism after the Reconquest rather than leave Spain—were suspected of being nominal Catholics who continued to practice Islam in secret. From 1609 through 1614, the Spanish monarchy forced an estimated 350,000 Moriscos to leave Spain for Muslim North Africa.

Today, up to five million descendants of the Moriscos are living in Morocco alone; there are millions more living in Algeria, Egypt, Libya, Mauritania, Tunisia and Turkey.

In a recent essay published by the Morocco-based newspaper Correo Diplomático, the Morisco-Moroccan journalist Ahmed Bensalh wrote that the "decision to grant Spanish citizenship to the grandchildren of the Hebrews in Spain in the fifteenth and sixteenth centuries, while ignoring the Moriscos, the grandsons of the Muslims, is without doubt, flagrant segregation and unquestionable discrimination, as both communities suffered equally in Spain at that time. The decision could also be considered by the international community to be an historic act of absolute immorality and injustice...This decision is absolutely disgraceful and dishonorable."

Bensalh then went on to threaten Spain: "Is Spain aware of what might be assumed when it makes peace with some and not with others? Is Spain aware of what this decision could cost? Has Spain considered that it could jeopardize the massive investments that Muslims have made on its territory? Does Spain have alternatives to the foreign investment from Muslims if they ever decide to move that capital to other destinations due to the discrimination against Muslims?"

Bensalh is one of many Muslim journalists, historians and academics who are demanding that Spain treat Moriscos the same way it treats Sephardic Jews.

Consider Jamal Bin Ammar al-Ahmar, an "Andalus-Algerian" university professor at the Ferhat Abbas University in Sétif in northeastern Algeria. Al-Ahmar has been engaged in a six-year campaign to persuade Spanish King Juan Carlos to identify and condemn those who expelled the Muslims from Al-Andalus in the fifteenth century. Al-Ahmar is also demanding that millions of descendants of the Moriscos expelled from Spain be allowed to return there.

In a letter addressed to the Spanish monarch, Al-Ahmar calls for a "full legal and historical investigation of the war crimes that were perpetrated on the Muslim population of Andalusia by the French, English, European and papal crusaders, whose victims were our poor miserable people, after the collapse of Islamic rule in Andalusia."

The letter speaks of "the injustice inflicted on the Muslim population of Andalusia who are still suffering in the diaspora in exile since 1492."

Al-Ahmar wants the Spanish monarch to apologize "on behalf of his ancestors" and to assume "responsibility for the consequences" this would entail. He says it is necessary "to identify criminals, to convict retroactively, while at the same time to identify and compensate victims for their calamities and restore their titles." This process would culminate with "a decree that allows immigrants to return to their homes in Andalusia, and grant them full citizenship rights and restoration of all their properties."

The Moroccan historian Hasan Aourid believes Spain has a policy of "double standards" vis-à-vis the Moriscos. Aourid—who recently wrote a novel, entitled "The Moriscos," to "remember the tragedy of those expelled from Al-Andalus"—told an audience at the Casablanca International Book Fair that Spain cannot become "reconciled with itself without recognizing its Moorish dimension" and asked if "the suffering was lower for Muslims than for Jews."

The Association for the Historical Legacy of Al-Andalus, a group dedicated to reviving the memory of the Muslim presence in Spain, says the Spanish government should treat Muslims and Jews the same way. By failing to offer Spanish citizenship to both groups, Muslims would become victims of "selective racism," said the president of the association, Bayib Loubaris.

Spain is unlikely to concede to these demands anytime soon. While few deny there are potentially millions of descendants of Moriscos living in North Africa today, the challenge lies in reconstructing reliable genealogies to determine legitimate heirs.

The issue of who is a Morisco and who is not will be a topic for discussion at a major international conference—"The Descendants of the Andalusian Moriscos in Morocco, Spain and Portugal"—to be held in Tangier from April 4-6, 2014.

But even if such genealogies could be compiled, calls to naturalize the descendants of expelled Muslims are sure to be opposed for another reason: the fact that the expulsion of the Muslims was part of a war to end the occupation of Spain by North African invaders.

Jose Ribeiro e Castro, a Portuguese lawmaker who drafted Portugal's law of return for Sephardic Jews, puts it this way: "Persecution of Jews was just that, while what happened with the Arabs was part of a conflict. There is no basis for comparison."