One significant distinction 1 was that the Spanish Inquisition was only one very notorious and extreme section of a much longer and geographically broad campaign by church officials from Rome to France, from Germany to England, to wipe out the scourge of medieval power that was heresy. What makes the Spanish auto-de-fe synonymous with this effort 2 was their immense refinement of the investigative, judicial and tribunal process. The legates and inquisitors essentially borrowed the immense legal infrastructure of medieval Scholasticism, with its intensely logical, almost geometric constructs, and then applied them to inherently illogical phenomena – namely human faith and sexuality.

    Though there had been active Inquisitions around Paris and Lombardy as early as the 1200s, things really got ‘roaring’ (if you’ll excuse that…and as pointed out by bozon above) in Spain after the forced conversion of the Jews and Moslem citizenry by Ferdinand and Isabella, after their successful re-establishment of a Christian fiefdom. That the Jews and Moslems had lived there almost five centuries, and were integral elements of the society, state, and economy, was not really up for debate. Given a choice between conversion or exile, most fled to Morocco or North Africa – but many converted, known as the converses - and it were these peoples, frequently of influential political or merchant families, which bore the real brunt of the Inquisition’s scrutiny.

    One night, after the first of the investigations had been set up, to examine the true faith of these new, ‘so-called Christians’, on September 15, 1485, Inquisitor Pedro Arbues was kneeling in prayer in a Saragossa cathedral, when eight long shadows moved among the dark pillars of the nave amid dim candle light. The next moment, Arbues was lying at the altar steps in a pool of blood, praying, dying from a dozen swift knife wounds. It was soon discovered the assassins had been hired by a frantic group of local converso families, who hoped to dissuade the investigation, but in the end only whipped up public support for the Church effort. However, the death galvanized Spanish opinion, and the murderers enjoyed the unusual dishonor of being hanged, drawn and quartered, AND having their hands lopped off and nailed to the cathedral doors. 3

    By 1492, Jews in the country were given a choice, a) convert, b) leave Spain with no more than you could carry on your back, or c) burn as a heretic. Never mind that this was completely un-Christian, and clearly contrary to Scripture, and even harmful to the laity of the faith in its coerced ‘faith’ and forced baptism – the rote answer from the Church for all these arguments was that freewill was clearly involved (albeit from some very unpleasant options) and therefore the sacrament of baptism was completely valid (the power of Christ compels you, the power of Christ compels you!). By 1502, the imposition of Catholicism was extended to the Moslem population; those who converted were known as the morisco.4

    But by 1512, the Inquisition itself was already under investigation for a wide range of bribery, corruption, patronage and wrong doing – even going so far as to recruit swindlers and burglars into their ranks to make the fleecing of rich heretics that much more efficient. Illuminism and Lutheranism both provided ample reasons to carry on the effort, with Cardinal Ximenez boldly leading the march. In 1551, local chapters of the Inquisition had been established in Toledo, Valencia, Granada and Seville – each began publishing long lists of auctores damnati, being those writers which could no longer be read by the faithful, and in 1558, printers and publishers were obliged to seek a license from a Church council. To print on the sly could be punished with death – Julian Hernandez was executed in 1560 just for smuggling books into Spain. Finally, in 1608, close to 300,000 Moslems were forcibly removed from Spain, which sparked a widespread collapse of argriculture, banking and trade-crafts. With a complete disappearance of a Spanish middle class, the country essentially receded into a neo-feudal society, just as the rest of Europe began to celebrate its 'Enlightenment'.
1 Which, god knows, escaped me for quite a while – who knew you could just go out and brand whole other religions automatically and instantly heretical, with just a simple papal bull?
2 Neglecting, however unwisely, for the moment, the incalculable influence of Monty Python’s Flying Circus’ The Spanish Inquisition Sketch.
3 One of the conspirators, upon hearing this, committed suicide in his cell by swallowing the glass shards of a broken lamp – so the Inquisitors sagely put his dead body through all the same tortures as his fellows, just to be ‘fair’.
4 A complete lack of Catholic priests with even a vague notion of Arabic, however, made the sincerity of the conversion policy laughable. For all this and more, see Henry Kamen, The Spanish Inquisition (Toronto: Mentor, 1965), pp. 52-121.