Гадячский договор
The establishment of the Grand Duchy of Ruthenia was considered at various times, particularly during the 1648 Cossack insurrection against Polish rule in primarily ethnically Ukrainian territories (see Khmelnytsky Uprising). Such a Ruthenian duchy, as proposed in the 1658 Treaty of Hadiach, would have been a full-fledged member of the Polish–Lithuanian Commonwealth, which would thereby have become a tripartite Polish–Lithuanian–Ruthenian Commonwealth. In May 1659, the Polish Diet (Sejm) ratified the treaty with an emended text.