Two decisions taken from Castile ended the arrangement the previous article describes.
The first was the Inquisition. Established in 1478 under Castilian and Aragonese authority, with papal authorisation, it was not directed at Muslims or Jews as such: its jurisdiction covered baptised Christians, and its target was the very large population of Jewish converts and their descendants, whose sincerity was in question after the mass conversions that followed the violence of 1391. That jurisdictional fact explains its procedures, its interest in domestic detail such as who lit lamps on a Friday evening, and its eventual reach into other kinds of suspect belief.
The second was the expulsion. In 1492, in the year Granada fell, the Catholic Monarchs ordered the Jews of their kingdoms to convert or leave. Estimates of how many left and how many stayed and were baptised vary widely, and Henry Kamen's revisionist history of the period argues that both the numbers and the character of the institution have been persistently exaggerated in the popular account while remaining serious enough on the evidence. The Muslims of Castile were required to convert a decade later, and the descendants of those converts were expelled between 1609 and 1614.
What left with the expelled was a whole religious civilisation, which reassembled around the Mediterranean and in the Netherlands, and which kept its Castilian speech for centuries as the language of prayer and of home.