Гадячский договор
Grand Principality of Rus' (Ukrainian: Велике Князівство Руське, Polish: Wielkie Księstwo Ruskie), also known in historiography as Grand Principality of Ruthenia, was the project of the state as a member of Polish–Lithuanian Commonwealth in the territory of Kiev Voivodeship, Bracław Voivodeship and Chernihiv Voivodeship. Its creation was proposed by Hetman Ivan Vyhovsky with Yuri Nemyrych and Pavlo Teteria in September 1658 during the negotiations between Cossack Hetmanate and Commonwealth. The project of the Duchy was approved in the first version of the Treaty of Hadiach, but later, because of the strong resistance of the Polish society, the idea of the "Grand Principality of Rus" was completely abandoned. The Cossacks were very disappointed with the final version of the treaty and The Ruin began. Yuri Nemirich, the alleged author of the "Grand Principality of Rus" project, was killed in a local fight in August 1659 and Vyhovsky lost his power in October 1659, thus the project did not become a reality.