Great changes were taking place at Saraï, in the Khan of the Golden Horde. Its power was broken by internal discord, when Mourout, the legal heir of Bati, was attacked by a rival Mamaï, who succeeded in establishing himself at Saraï. Simeon was succeeded by his brother, Ivan II, an easy-going, good-natured man whose reign of six years did not increase the influence of Moscow. At his death, in 1359, he left several minor children, the oldest of whom was Dmitri, a boy of twelve. Dmitri of Souzdal went to Saraï--and secured the iarlikh, which made him Grand Duke of Vladimir, but Alexis, the Metropolitan, was loyal to Ivan's children, and appealed to the khan in the name of his young ward. Mourout, the heir of Bati, declared in his favor, (p. 090) and young Dmitri was taken to Vladimir escorted by an army, and installed. (1363.)
The appointment was disputed by the dukes of Tver, Souzdal, and Riazan. Dmitri of Souzdal held an iarlikh from Mourout's opponent, and tried to enter in Vladimir, but was expelled. The Metropolitan excommunicated the opponents of Ivan's son, who held the fort as Grand Duke. Young Dmitri made war upon the Duke of Tver, and after a seven years' struggle (1368-1375), compelled him to renounce his claims.
Dmitri was summoned before the Khan, in 1371. He went but what he saw at Saraï convinced him that the Tartars were no longer able to uphold their authority. He did not hesitate to engage in a struggle with Riazan, although it was supported by a Tartar army. Thereafter, when orders arrived from the khan, Dmitri ignored them. In 1376, he sent a large army to Kazan on the Volga, and forced two Mongol chiefs to pay tribute. Two years later, in 1378, a battle was fought between Dmitri and one of Mamaï's generals in Riazan, when the Tartars were defeated, which made the grand duke exclaim: "Their time is come, and God is with us!" The khan sent an army to ravage Riazan, and made preparations to reëstablish his authority at Moscow.
To make sure of success, Mamaï took two years to collect an immense army and to mature his plans. This could not remain secret to the Russians, who, aroused by Dmitri, laid aside their private feuds to make common cause against the infidels. A large number of dukes assembled at Moscow, and even the Lithuanians promised to send (p. 091) troops to Kostroma where the Russian army was gathering. The Metropolitan assured Dmitri of the victory, and sent two monks to go with the troops. Making the sign of the Cross on their cowls, he said, "Behold a weapon which faileth never!"