We know little of the rule of Ivan Kalita, but this little tells us of his talents. As the chroniclers said, when he became the grand knyaz, "great calmness came to the Russian land for forty years, and the Tatars stopped fighting the Russian land". Probably, it was Kalita who obtained the permission from the Mongols to bring the tribute to the Golden Horde, without the Mongol tribute collectors. So, the Mongols almost stopped to come to Rus. Since this was one of the main causes of numerous rebellions, the social peace was established in Rus. The legends say also that Kalita cleared Rus of robbers and thieves. The social order and peace attracted new settlers to Rus. The main political achievement of Kalita was that he convinced the metropolitan of Rus to move to Moscow.
After the decline of Kiev, the church leadership had to decide whether they should stay in Kiev or to look for a new location. About 1300, after Mongols raided Kiev again, the metropolitan Maxim moved to Vladimir. After that, the knyazes of Galich asked the Constantinople patriarch to establish a new metropoly in south-western Rus. The patriarch refused to split the Russian church. After the death of Maxim, he appointed hegumen (abbot) Peter, who was born in Volyn (near Galich), the new metropolitan. When Peter came to Kiev, he soon followed Maxim and moved to the north, too. Officially, his residence was in Vladimir. However, this city had already lost its importance and the was contested by Moscow and Tver. Peter supported Moscow and Ivan Kalita. He lived often in Moscow, founded the Uspensky cathedral in Moscow. His successor, Greek Theognostos, finally chose Moscow his residence and made Moscow the official capital of the Russian church. So, Moscow became both political and religious center of Rus. The status of the grand knyaz obtained by Kalita gave him support of the boyars, too, since their position at the court of the grand knyaz was more prestigious than in other principalities.
Under the rule of Ivan Kalita (1328-1341) and his sons Simeon the Proud (1341-1353) and Ivan the Red (1353-1359), Moscow began to overcome the neighboring principalities. They demonstrated that they can support peace not only in their appanage, but in the whole Vladimir-Suzdal principality. The social peace was so important for the population of the bordering lands, that they eagerly joined the duchy of Moscow.
After Theognostos moved to Moscow, he chose and prepared a heir for himself -- a Muscovite Alexy, an offspring of a noble family of Pleshcheyevs. During the rule of Ivan the Red, who was a weak ruler, and his little son Dimitry, Alexy virtually ruled the duchy of Moscow. Multifaceted talents of Alexy earned him respect in the Golden Horde, where he healed the eyes of Taidula, a khan's wife. In the Russian politics he consistently backed the leadership of Muscovy. He and his followers propagated the perception of the power as the state established by god. The strength of Muscovy was very important for their plans to unite the lands under one strong ruler. After Alexy a monk named Sergii (Sergius), the founder of the famous Troitsky (Trinity) monastery (now Troitse-Sergiyeva Lavra 70 kilmetres north from Moscow), continued his policy and supported the knyazes of Moscow.
Muscovy was protected from foreign invasions by border principalities (Ryazan, Nizhny Novgorod, Smolensk, etc.), it was in peace with the Golden Horde and retained social peace. This security attracted people to Moscow. The knyazes of Moscow built new villages and towns for the newcomers, liberated Russians enslaved by Mongols and brought them to their lands. Their policy was directed at the growth of the population.
So, the first successes of the knyazes of Muscovy and their rise above other principalities brought them support of the aristocracy, the religious leaders and the population of the neighboring lands. Till the end of the XIV century, under Ivan Kalita and his sons, the growth was more or less occasional. Later, when the Moscow knyazes became the protectors of Rus against the Horde and Lithuania, Moscow became the centre of the national unification, and the knyazes of Muscovy became the national leaders.