[16] The Rus' principalities and neighbouring states frequently changed their allegiancies at this time, joining forces with or against various Mongol factions and with or against each other, in tactical efforts to exploit rapidly shifting situations.

[8] The Grand Duchy of Lithuania as well as Horde vassals such as Tver and Muscovy were opportunistic in profiting from the internecine warfare that weakened Mongol-Tatar control in the region.

[18] However, Tokhtamysh's lightning rise to power in the late 1370s, his definitive victory over Mamai (1381) and subsequent sack of Moscow (1382) confirmed the Rus' principalities' vassalage to the Golden Horde.

[19] The Golden Horde had reached the height of its power and prosperity under Özbeg Khan (r. 1313–1341), when overland trade from the Black Sea to Yuan dynasty China flourished.

[citation needed] While Özbeg adopted Islam, the Orthodox Church (exempt from taxes through yarliks or patents[20]) continued supporting his rule, and the Turco-Mongolian population of his realm gradually assimilated and became known as "Tatars".

[citation needed] Taxes regularly collected by the darughachi or basqaq (baskak) from the subordinate Rus' principalities provided the Horde's coffers with plenty revenue.

[22] They employed this highly symbolic title to prop up a weaker Rus' principality (usually Muscovy) against a stronger one (usually Tver) to keep the latter in check as a divide and rule policy.

[22] In the mid-14th century, Algirdas (Olgerd) of Lithuania would try to bring Tver and Ryazan under his control during the Lithuanian–Muscovite War (1368–1372), and also played by the Mongol rules by sending a delegation to Golden Horde (as the neutral power-broker) in order to negotiate peace.

[24] When Qulpa was killed (1360) by yet another brother, Nawruz Beg, who himself died under suspicious circumstances after a year on the throne, the lineage of Batu Khan (the 1242 founder of the Golden Horde) went extinct.

[citation needed] When Rus' princes heard of Berdi Beg's death, they had begun travelling to Sarai to receive patents from his successor, but by the time they arrived, Nawruz had already assumed the throne.

[31] The siege of Moscow in 1382 was motivated by khan Tokhtamysh's desire to punish Muscovy for its audacity to challenge the authority of the Golden Horde at the Battle of Kulikovo (1380).

[f][34] The princes of Nizhniy Novgorod tricked the population into surrendering the city, after which Tokhtamysh' forces immediately sacked Moscow as punishment for resisting Mongol authority.

[32] Although Kulikovo had marked Muscovy's new position as the pre-eminent state amongst the Rus' principalities,[8] the subsequent sack of Moscow confirmed that Donskoy and the other princes remained firmly under suzerainty of the Tatar–Mongol Golden Horde, now ruled by Tokhtamysh.