I have been thinking about Columbus and Isabella. To me it looks like the war against Moorish rule in Spain was connected with the expulsion. The thing which looks odd is that Isabella looks  heroic in her support of Columbus, even pledging her crown jewels to pay for the expedition, [that was said to be a suicide mission by all the experts.] The message got to her just as she and her husband were about to wage the last battle to end Moorish rule in Spain. But she does not seem so nice when the issue was the Alhambra decree. 

  However I think it is possible to understand Isabella by means of  the way the Columbus himself thought of his mission was as a  way of expanding Christianity. [There is lots of evidence for this.] So I think to understand Isabella is clear. She wanted Spain to be Christian and she wanted to expand Christianity.

I think this is clear also from the events starting from the pogrom of 1391 which started the downward spiral. There were plenty of converts [about 200,000] and it seems many of which were not sincere. So you have the Inquisition which was directly responsible for investigation of insincere conversions. The numbers of auto-de-fa's are not as great as people imagine. The estimates are between 1000 and 2000. Still the pressure was on.