Early Finnish saga 5.

Swedish–Novgorodian Wars were a series of conflicts in the 12th and 13th centuries between the Republic of Novgorod and medieval Sweden over control of the Gulf of Finland, an area vital to the Hanseatic League and part of the Varangian-Byzantine trade route. 

The Swedish attacks against Orthodox Russians had religious overtones, but before the 14th century there is no knowledge of official crusade bulls issued by the pope.

Scandinavians maintained trade relations and other links with Novgorod from the Viking Age onwards. Merchants from Gotland operated both their own trading house (Gutagård) and the St. Olof church in Novgorod. 

Scandinavians also carried out isolated raids on Novgorod. Eiríkr Hákonarson raided Ladoga in 997, and his brother Sveinn Hákonarson followed suit in 1015. After the marriage of Yaroslav I (Grand Prince of Novgorod and Kiev) to Ingegerd of Sweden in 1019, Ladoga became a jarldom in the orbit of Kievan Rus. 

Eirikr Hakonarson
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Ragnvald Ulfsson 

The major turning point into more permanent conflict between Sweden and Novgorod arrived with Sweden's firmer organization into the Catholic Church in the 12th century and papal involvement in crusades against lands controlled by the Orthodox Church.

It was ruled by Ragnvald Ulfsson, the alleged father of King Stenkil of Sweden (reigned 1060-1066). Dynastic marriages took place between Russian and Scandinavian royal families - for example, in the 1090s Stenkil's granddaughter Christina married Mstislav of Novgorod, upon whose death in 1132 Novgorod seceded from Kievan Rus.
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Apart from Ladoga, Novgorodian interests clashed with Sweden's in Finland, a country which Russian forces sacked on numerous occasions from the 11th century onward. The raid in the winter of 1226-1227 led to heavy losses on the Finnish side.

A Finnish retaliatory raid against Ladoga in 1228 ended in defeat, contributing to the Finns' subjugation by the Catholic Swedes during the Second Swedish Crusade in 1249. Seven years later, the Novgorodians devastated Swedish Finland again.

In 1293 the Swedes won a part of western Karelia and built the fortress of Viborg (Russian: Vyborg) there. This expedition has traditionally been dubbed as the Third Swedish Crusade. Seven years later, they founded the fortress of Landskrona in the mouth of the Neva, on the river Okhta, and ruined the Novgorod settlements on the Neva. Later that year, the Novgorod troops retaliated by destroying Landskrona.

In the early 14th century, military tensions escalated and the two powers were continually at war. In 1311, the Novgorodians devastated central Finland, where the Swedes had recently built a new castle. In response, a Swedish fleet embarked towards Ladoga and set that trade emporium on fire. Three years later, the Karelians' discontent with Novgorod's rule broke out into the open, as they killed Russian governors and sought help in Sweden. After several months of hostilities, Karelia submitted to Novgorod's authority again.

In 1318 Novgorod attacked Turku in southwestern Finland, burning the city and the cathedral as well as the episcopal castle in Kuusisto Castle. Four years later, they besieged Viborg and founded Oreshek, an important fortress dominating the entrance to Lake Ladoga.