According to the Spanish Monarchs Ferdinand and Isabella, the Conversos were the primary reason for their fateful decision to eventually order the expulsion of Jews in 1492 from their Iberian and overseas dominions. Scholars have argued what the motivations were for this decision. I believe the role of the “Converso problem” should not be underestimated.
For comparison, we may look to the case of Jews in England at the end of the 13th century. While the primary motivations for expelling Jews from England was economic, objections were also raised as to the influence they had over Jewish converts to Christianity who were returning to, or continuing to practice Jewish rites.
Cecil Roth notes: “Among the reasons given for the expulsion of the Jews from England in 1290 was that they persisted in seducing recent converts to return to the ‘vomit of Judaism.’ Ancient Jewish authorities add that many children were kidnapped and sent to the north part of the country, where they long continued their ancestral religious practices.”1
For the text of the Expulsion order, see The Edict of Expulsion
By Rabbi Juan Bejarano-Gutierrez the director of the B’nei Anusim Center for Education and author of What is Kosher?
1 Cecil Roth, A History of the Marranos, (Jewish Publication Society, Philadelphia, 1947), 8-9.