https://en.m.wikipedia.org/wiki/Battle_of_Kulikovo#BattleOn September 8, 1380, the Battle of Kulikovo took place. Moscow's great monarch Dimitri defeated the Mongols beginning the decline of the Tatars. From the article:
"After the Mongol-Tatar conquest, the territories of the disintegrating Kievan Rus became part of the western region of the Mongol Empire (also known as the Golden Horde), centered in the lower Volga region. The numerous Russian principalities became the Horde's tributaries. During this period, the small regional principality of Moscow was growing in power and was often challenging its neighbors over territory, including clashing with the Grand Duchy of Ryazan. Thus, in 1300, Moscow seized the city of Kolomna from Ryazan, and the Ryazan Prince was killed after several years in captivity.[7]
After the killing of Khan Berdi Beg of the Golden Horde at 1359, a civil war had arisen there. Warlord (temnik) Mamai, who was son-in-law and beylerbey of Berdi Beg, soon took the power in the western part of the Golden Horde. Mamai enthroned Abdullah Khan in 1361 and after his mysterious death in 1370 immature Khan Muhammad Bolak was enthroned.[8] Mamai was not a Genghisid (descendant of Genghis Khan), and as such his grip on power was tenuous, as there were true Genghisids with claims to mastery. Therefore, he had to constantly fight for supreme power and at the same time struggle against separatism. While there was a civil war in the falling Golden Horde, the new political powers were appearing, such as the Grand Duchy of Lithuania, the Grand Duchy of Moscow, and the Grand Duchy of Ryazan.
Meanwhile, the Grand Duchy of Lithuania continued its expansion. It competed with Moscow for supremacy over Tver and in 1368-1372 made three campaigns against Moscow. After the death of Algirdas in 1377, his eldest sons Andrei of Polotsk and Dmitri of Bryansk began to struggle with their step-brother Jogaila for their legitimate right to the throne and entered into an alliance with the Grand Prince of Moscow.[9]
Simultaneously with the beginning of the Great Troubles in the Horde in 1359, Prince of Moscow Ivan II died and the new Khan of the Horde by his jarliq (law pronouncement) transferred the throne of the Grand Duchy of Vladimir to the Prince of Nizhny Novgorod. But the Moscow elite (in 1359, new Prince Dmitry was only 9 years old) did not accept this. They used equally armed force and bribes to various Khans and as a result, in 1365, forced the princes of Nizhny Novgorod to finally give up claims to the Grand Duchy of Vladimir.[8] In 1368, the conflict between Moscow and Tver began. Prince of Tver Mikhail used the help of Lithuania, and in addition, in 1371 Mamai gave him a jarliq to the Grand Duchy of Vladimir. But the Moscow troops simply did not let the new "Grand Prince" enter to Vladimir, despite the presence of the Tatar ambassador. The campaigns of the Lithuanian army also ended in failure and so the jarliq returned to Dmitry. According to the results of the truce with Lithuania in 1372, the Grand Duchy of Vladimir was now recognized as the hereditary possession of the Moscow Princes.[10] In 1375 the Prince of Tver once again received a jarliq for the Grand Duchy from Mamai. Then Dmitri with a strong army (larger than it was in the Kulikovo battle) quickly moved to Tver and forced it to capitulate. Mikhail recognized himself as the "little brother" of the Moscow Prince and ensure to participate in wars with the Tatars.[11]
The open conflict between Dmitry and Mamai began in 1374, the exact reasons are unknown. It is believed that the illegitimacy of the puppet khans of Mamai was by that time too obvious, and he demanded more and more money, as he lost the war for the throne of the Golden Horde.[12] In the following years the Tatars raided Dmitry's allies and the Moscow troops made campaign against Tatars over the Oka River in 1376 and seized the city Bolghar in 1377. In the same year "Mamai's tatars" defeated the army of Nizhny Novgorodl with an auxiliary detachment left by Dmitry at the Battle on Pyana River. The Tatars then began to raid Nizhniy Novgorod and Ryazan.[13]
Mamai continued attempts to re-affirm his control over the tributary lands of the Golden Horde. In 1378, he sent forces led by the warlord Murza Begich to ensure Prince Dmitri's obedience, but this army suffered crushing defeat at the Battle of the Vozha River. Meanwhile, another khan, Tokhtamysh, seized power in the eastern part of the Golden Horde. He enjoyed the support of Tamerlane and was ready to unite the entire Horde under his rule. In 1380, despite the threat from Tokhtamysh, Mamai chose to personally lead his army against the forces of Moscow. In preparation for the invasion, he entered into an alliance with Prince Jogaila of Lithuania. Ryazan Prince Oleg was defeated by Mamai in 1378 (and his capital was burnt), he had no strength to resist Mamai, and Ryazan's relationship with Moscow had long been hostile. Therefore, in the campaign of 1380 Oleg took the side of Mamai, although this fact is sometimes challenged. Mamai camped his army on the bank of the Don River, waiting for the arrival of his allies."