In 1221, Pope Honorius III was again worried about the situation in the Finnish-Novgorodian Wars after receiving alarming information from the Archbishop of Uppsala. He authorized the Bishop of Finland to establish a trade embargo against the "barbarians" that threatened the Christianity in Finland. The nationality of the "barbarians", presumably a citation from Archbishop's earlier letter, remains unknown, and was not necessarily known even by the Pope. However, as the trade embargo was widened eight years later, it was specifically said to be against the Russians. Based on Papal letters from 1229, the Bishop of Finland requested, the Pope enforce a trade embargo against Novgorodians on the Baltic Sea, at least in Visby, Riga and Lübeck. A few years later, the Pope also requested the Livonian Brothers of the Sword send troops to protect Finland. Whether any knights ever arrived remains unknown.
Hoping to exploit Novgorod's weakness in the wake of the Mongol and Swedish invasions, the Teutonic Knights attacked the neighboring Novgorod Republic and occupied Pskov, Izborsk, and Koporye in autumn 1240. When they approached Novgorod itself, the local citizens recalled to the city 20-year-old Prince Alexander Nevsky, whom they had banished to Pereslavl earlier that year. During the campaign of 1241, Alexander managed to retake Pskov and Koporye from the crusaders.
In the spring of 1242, the Teutonic Knights defeated a detachment of Novgorodians about 20 km south of the fortress of Dorpat (Tartu). Led by Prince-Bishop Hermann of Dorpat, the knights and their auxiliary troops of local Ugaunian Estonians then met with Alexander's forces by the narrow strait (Lake Lämmijärv or Teploe) that connects the north and south parts of Lake Peipus (Lake Peipus proper with Lake Pskovskoye).