As Lithuania expanded eastward during the 14th century, it absorbed large portions of former Kievan Rus', including Kyiv, Smolensk, and Chernigov, establishing control over a vast Ruthenian population. However, with the rise of the Grand Duchy of Moscow, which began unifying Russian principalities after the decline of the Golden Horde, Lithuania’s eastern front became a battleground. Moscow sought to reclaim these former Orthodox territories and expand westward, posing a growing threat to Lithuania's territorial integrity.
Muscovite ambition to consolidate lands once ruled by Kievan Rus' became evident during the reign of Ivan III ("Ivan the Great"). By the late 15th century, Moscow's influence was rising, fueled by the collapse of the Mongol yoke. Ivan III styled himself as the sovereign of all Russia and claimed a right to the territories now under Lithuanian control. This ideological expansion sparked a series of wars beginning in 1487, shortly after Lithuania’s border reached within 100 miles of Moscow. Over the next few decades, Lithuania would suffer territorial losses, culminating in the loss of Smolensk and other key regions.
The first major war (1487–1494) saw Moscow seize territories along the border, capitalizing on Orthodox nobles’ dissatisfaction under Lithuanian rule. Lithuania ceded Vyazma and other lands in a peace treaty in 1494, marking its first significant territorial loss.
The second war (1500–1503) dealt another devastating blow. Moscow, accusing Lithuania of persecuting Orthodox subjects, launched an invasion. Lithuanian forces suffered a decisive defeat at the Battle of Vedrosha in 1500, leading to the loss of Chernihiv, Novgorod-Seversk, and Starodub, reducing Lithuania’s eastern frontier by a third.
A third conflict in 1507–1508 was entangled with Glinsky's Rebellion, a Lithuanian noble revolt. Although the rebellion ultimately failed, it further weakened Lithuania, which was forced to accept the status quo of 1503 through an inconclusive truce.
The fourth war (1512–1522) saw Moscow’s forces capture Smolensk in 1514, despite Lithuania’s victory at the Battle of Orsha that same year. Smolensk would remain under Muscovite control despite several attempts to recapture it. The peace of 1522 cemented Lithuania’s territorial losses and recognized Moscow’s dominance over former Lithuanian lands.
Following the death of Vasili III of Moscow, political instability in Moscow gave Lithuania an opportunity to reclaim lost ground in the Fifth War (1534–1537) . Lithuania allied with Polish forces and the Crimean Tatars to launch a counteroffensive, successfully seizing Gomel and Starodub. However, the truce of 1537 granted Moscow control of key border fortresses, preventing Lithuania from fully reversing its territorial setbacks.
The Muscovite–Lithuanian wars exposed Lithuania’s military vulnerabilities and increasingly pushed it toward closer cooperation with Poland. As Moscow grew more powerful and asserted itself as the successor to Kievan Rus', Lithuania's reliance on Polish aid deepened, laying the groundwork for the eventual Polish–Lithuanian Commonwealth in 1569. Additionally, the wars displaced Lithuania’s center of power westward, shifting focus from eastern Ruthenian lands to safeguarding Lithuania's core territories against the dual threats of Moscow and the Crimean Tatars.
In this context, the Jagiellonian dynasty's union with Poland became not just a strategic necessity but a matter of survival. As Lithuania fought to defend its autonomy and contain Moscow’s westward expansion, the growing alignment with Poland shaped the trajectory of both states for centuries to come.