King and priest were thus natural allies as against the freemen or the chieftains in each territory; and the advance of the Church was bloody or bloodless according as the king was able to enforce his will. In the Scandinavian countries the founding of Christianity was a life-and-death struggle, lasting in all for some two hundred and fifty years (820-1075), between the local liberties, bound up with pagan usages, and the centralizing system of the Church. Again and again the Church was overthrown, with the king who championed it; and the special ferocity of the marauding vikings against Churchmen wherever they went seems to have been set up by their sense of the Church's monarchic function. The fact that many priests were ex-serfs made them the more obnoxious; and they in turn would strive the more zealously for the Church's protecting power. But the Church's political work did not end with the humbling of the vikings, as such, at the hands of the kings who finally mastered them; it endorsed the aggressive imperialism of the Danish king Knut as it had done that of Rome; and never till the time of the Crusades does the ostensible universality of the Church seem to have checked the old play of racial hatreds and the normal lust of conquest. So clearly did Charlemagne realize the political use of the Church that, while he imposed it everywhere in his own dominions, he vetoed its extension to Denmark, where it would be a means of organizing a probably hostile power, many of the stubborn Saxons having fled thither. From the moment of its establishment it had been stamped with the principle of political autocracy; and only when its own mounting power and wealth made it a world-State in itself did it restrain, in its own interest, the power of kings. In the earlier stages, king and Church supported each other for their own sakes; and it was as a political instrument, whose value had been proved in the Roman Empire, that the Church was sooner or later accepted by the barbarian kings. All the while popes and prelates complained bitterly that many of the converts thus won were baptized and rebaptized, yet continued to live as heathens, slaying priests and sacrificing to idols. When, however, open heathenism was beaten down, the combined political and religious prestige of the Christian priest gave him a hold over the multitude, forever superstitious, such as those of the heathen times had never wielded save in Gaul. To the new regal tyranny was added that of the Church. When the Servians, who had been nominally Christianized under the rule of Byzantium in the eighth century, regained their independence in the ninth, they significantly renounced Christianity; and only after re-conquest were they again "converted." To this day their old pagan beliefs abound under cover of Christianity.