The centralisation movement, that began in the fifteenth century, and that tended to increase the power of the sovereign at the expense of the lesser nobles and of the people, was strengthened and developed by the religious revolt. The Protestant reformers appealed to the civil rulers for assistance against the ecclesiastical authorities, and in return for the aid given to them so generously they were willing to concede to the king all power in civil and ecclesiastical matters. Thenceforth the princes were to be so supreme in spirituals as well as in temporals that their right to determine the religion of their subjects was recognised as a first principle of government. During the days of the Counter-Reformation, when religious enthusiasm was aroused to its highest pitch, the Catholic sovereigns of Europe fought not so much for the aggrandisement of their own power as for the unity of their kingdoms and the defence of the religion of their fathers, threatened as it was with complete overthrow. But once the first fervour had passed away, and once it was recognised that religious harmony could not be secured by the sword, Catholic sovereigns began to understand that the Protestant theory of state supremacy meant an increase of power to the crown, and might be utilised to reduce the only partially independent institution in their kingdoms to a state of slavery. Hence they increased their demands, interfered more and more in ecclesiastical matters, set themselves to diminish the jurisdiction of the Pope by means of the /Royal Placet/ and other such legal contrivances, and asserted for themselves as much authority as could be reconciled with Catholic principles interpreted in their most liberal sense. They urged the bishops to assert their independence against the Holy See, and the bishops, forgetful of the fact that freedom from Rome meant enslavement by the State, co-operated willingly in carrying out the programme of their royal masters. Men like Bossuet, carried away by the new theories of the divine right of kings, aimed at reducing the power of Rome to a shadow. They were more anxious to be considered national patriots than good Catholics. They understood only when it was too late that in their close union with the Holy See lay their only hope of resisting state aggression, and that by weakening the authority of the Pope they were weakening the one power that could defend their own rights and the rights of the Church. Their whole policy tended to the realisation of the system of national churches, and were it not for the divine protection guaranteed by Christ to the society that He Himself had founded, their policy might have been crowned with success.