4 ideas
In 1391, anti-Jewish riots that began in Seville spread across Castile and Aragon; many Jews were killed and many more converted under threat, creating a large class of conversos. Converts who rose in the church, commerce and government then drew popular suspicion, and blood-purity statutes such as Toledo's in 1449 recast the problem from religion to lineage.
When a majority forces a minority to convert, the old boundary of belief disappears, so suspicion moves to ancestry and hidden identity. Mass conversion therefore does not end persecution. It creates a new category of suspect insiders, defined by descent under 'limpieza de sangre' rules, that no act of faith can escape.
The celebrated coexistence of al-Andalus and early Christian Spain worked through protected-but-subordinate status: dhimmi rules under Islam and royal 'serfs of the treasury' status under Christian kings. Jews thrived as courtiers, physicians, translators and tax farmers because rulers found them useful. That same dependence on the ruler made their security depend on royal favor and fiscal need, so tolerance could collapse when those shifted.
After 1492, expelled Jews carried Spain with them as a cultural homeland rather than a territory. Exile thus made the expelling country a permanent element of the victims' identity, and Sephardim often stood apart from local Jewish communities they joined.