The metropolitan could exert his influence everywhere. Thus Theognost closed the churches at Pskov when that city offered an asylum to Alexander Mikhailovitch, and St. Sergius did likewise at Nijni-Novgorod when it accepted a prince to whom Moscow was opposed. This alliance was a most natural one: if the princes needed the authority of the church, the clergy--at that time the representatives of the most advanced ideas concerning the civil order--sought to realise that order of which it stood in need even for its purely economic interests. There is not the slightest doubt that one of the chief causes of the devotion of the clergy to the views and policies of the Muscovite princes, lay in its conviction that it was bound to derive material advantages from the concentration of all power in the hands of one prince. In fact, while the system of appanages prevailed, it was, on the one hand, extremely difficult for the clergy to enjoy its possessions and privileges in security, because the maintenance of this security depended not on one, but on many; while on the other hand, the princes of appanages infringed on clerical privileges more frequently than the grand prince. The dispersion of the monastic estates over several principalities still further contributed to the desire of the clergy for the abolition of the appanage system, which increased the difficulties of managing those estates. Especially in the case of war among the princes of appanages, the clergy of one appanage might easily be deprived of its possessions in another appanage, because at such a time all means of injuring the enemy were considered permissible. In the increase of power of the Muscovite princes a leading part also belongs to the Moscow boyars, whose activity was principally displayed during the youth or minority of the grand princes.[23] Such were the principal causes of the strength of the Moscow princes; to them should be added (according to the historians N. V. Stankevitch and S. M. Soloviov) the central position of the principality of Moscow, both in the sense that Moscow is near the sources of the chief rivers, and that an attack from without must first fall on the surrounding principalities. But these causes are evidently secondary and would have no significance without the others: Moscow is not so far from the other principalities that these advantages would belong to her alone. It was much more important that a wise policy, by preserving Moscow from the attacks of the Tatars, attracted thither an increased population and thus enriched the principality. A final important cause was the weakening of the Tatar horde and its dismemberment at the end of this period, of which the princes of Moscow did not fail to take advantage for their own ends.[b] THE INFLUENCE OF TATAR DOMINATION