The origins of the conflict that led to the battle of Lake Peipus in 1242 are unclear and controversial. An influential historiographical tradition has sought to link it to three earlier clashes in the region, all of which
Aleksandr Yaroslavich was involved in: the alleged July 1240
Battle of the Neva (only attested in Rus' sources), the September
1240 Izborsk and Pskov campaign, and the winter
1240–1241 Votia campaign. Researchers have endeavoured to look for Swedish motives to advance into the
Neva river basin, often by reference to the letter which
Pope Gregory IX sent to the archbishop of Uppsala at the end of 1237, suggesting that a crusade should be held in southwestern Finland against the
Tavastians, who allegedly reverted to their pagan beliefs. On the assumption that a successful 'anti-Tavastian crusade' took place in 1238–39, the Swedes would have advanced further east until they were stopped by a Novgorodian army led by Alexander Yaroslavich, who defeated them in the Battle of the Neva in July 1240, centuries later receiving the nickname
Nevsky. Nevertheless, this hypothesis resulted in numerous unresolved issues. If the battle did take place, it was probably only a minor clash, in which religion played no role. Novgorod would have fought against this incursion to protect their monopoly on the Karelian fur trade, and for access to the
Gulf of Finland. Novgorodians had been attempting to subjugate, raid and convert the pagan Estonians (known as
Chud) since 1030, when they established the outpost
Yuryev (modern
Tartu). From the late 12th century, German-Livonian missionary and crusade activity in Livonia and Estonia caused tensions with the Novgorod Republic. The Estonians would sometimes ally with various Rus' principalities against the crusaders, since the eastern Baltic missions constituted a threat to Rus' interests and the tributary peoples. After Novgorod tried to subjugate
Lett tribes south of Yuryev in 1212, the
Livonian Brothers of the Sword captured Yuryev in 1224, which became the
Bishopric of Dorpat's capital. The 1224 peace treaty that the Livonians signed with Pskov and Novgorod was in the latter's favour, and family ties were soon established: prince (died 1227) married off his daughter to Theoderic of Buxhövden, brother of bishops
Albert of Riga and
Hermann of Dorpat. Vladimir's son Yaroslav would later attempt to become the new prince of Pskov with the help of his brother-in-law, bishop Hermann of Dorpat; they failed in 1233, but succeeded during the September
1240 Izborsk and Pskov campaign. Some time after, in the winter of 1240–1241, the combined forces of the
Bishopric of Ösel–Wiek (in modern-day western Estonia) and the
Livonian Order launched the
1240–1241 Votia campaign. This campaign may be properly considered a crusade in the sense of a missionary conquest of 'pagan' lands. It is unknown whether
Votia was a tributary of Novgorod at the time, or only became one later. In either case, while the Sword Brothers and bishop Henry of Ösel–Wiek probably did not intend to attack Novgorod, their actions provoked a Novgorodian counterattack in 1241. The delayed response was a result of the internal strife in Novgorod. During the campaign of 1241, Alexander managed to retake both Votia and Pskov. Alexander then continued into Estonian-German territory. In the spring of 1242, the Teutonic Knights defeated a detachment of the Novgorodian army about south of the fortress of Dorpat (now
Tartu). As a result, Alexander set up a position at
Lake Peipus, where the battle would take place on 5 April 1242. == Accounts in primary sources ==