Canon Law on one side and the rise of cities on the other shattered the position of the Jews until they were reduced to sore straits at the end of the Middle Ages. The church labored persistently and relentlessly through the centuries in which Europe was thoroughly Christianized, to separate the Jews as far as possible from their Gentile neighbors. The ties which united the two parts of the population by a thousand threads of mutual interest, friendship, co-operation and beneficial intercourse, were slowly loosened and, where possible, all but severed. At the various Church Councils, from Nicea to the last Lateran, there was laid down the theory of the necessity to force the Jews out of the national life of the countries in which they dwelt, and to segregate them as a distinct, inferior and outlawed class. The principles enunciated by the higher clergy were disseminated by the priests and the demagogues among the masses. Special laws and restrictions were often followed by attacks, sacking of the Jewish quarters and degradations of various kinds. In the twelfth and the following three centuries the ill-treatment was often followed by expulsions and cancellation of debts, while heavy fines on individual Jews or on entire communities were accepted on both sides as a lesser evil or as easy terms for escaping greater hardships. The climax of this method of dealing with the Jews, the greatest blow administered to the unhappy Children of Israel by Christian princes, was the expulsion from Spain in 1492, and its concomitant, the expulsion from Portugal five years afterwards. But the Church alone could never have accomplished the ruin of the Jews if the changing economic conditions and the rise of a large and powerful class of Christian merchants did not help to undermine the position of the erstwhile solitary trading class. The burgher classes were the chief opponents and persecutors of their Jewish competitors: they seconded, and in many cases instigated, the efforts of the clergy to exclude the Jews from many occupations. So when the city overpowered the land owner and began to exert a preponderant influence on the government, the cause of the Jew was lost, or at least postponed until a more humane and liberal time, when the ordinary claims of the brotherhood of man were to overcome the narrow-minded mercantile and ecclesiastical policies of a ruder age. The great historian Ranke pointed out that the struggle between the cities and the nobility in Castille was decided in favor of the former by the marriage of Queen Isabella to Ferdinand of Aragon. It was also this marriage which sealed the doom of the Spanish Jews, as well as that of their former friends and protectors, the Moors, who had by that time sunk so low, that it was impossible for them to keep their last stronghold in Europe much longer.