The work is devoted to one of the directions of medieval diplomatic history: the struggle of the principalities of North-Eastern Russia (Moscow, Tver, Nizhny Novgorod), the Russian-Lithuanian state, as well as the Russian Orthodox Church for priority in the reunification of Russian lands and the role of the so-called "Byzantine factor" in the formation of Russian statehood. In the center of the story is the Grand Duchy of Moscow at the end of the 14th - middle of the 15th centuries, that is, the period of the reign of the Grand Dukes of Moscow Vasily I (1389-1425) and Vasily II (1425-1462).