Karelian language
In the regions ruled by Novgorod, the protolanguage started to evolve into Karelian language. In 1617 Novgorod lost parts of Karelia to Sweden in the Treaty of Stolbovo, which led the Karelian-speaking population of the occupied areas to flee from their homes. This gave rise to the Karelian speaking population in the Tver and Valday regions.