Treaty of Hadiach
Thought was given at various times to the creation of a Grand Duchy of Ruthenia, particularly during the 1648 Cossack insurrection against Polish rule in Ukraine. Such a Duchy, as proposed in the 1658 Treaty of Hadiach, would have been a full member of the Commonwealth, which would thereupon have become a tripartite Polish–Lithuanian–Ruthenian Commonwealth, but due to szlachta demands, Muscovite invasion, and division among the Cossacks, the plan was never implemented.