Гадячский договор
"1657-59: Vyhovsky and the Poles:" At the time of Khmelnitsy's death his son Yurii was only 16, so the hetmanate was given to Ivan Vyhovsky (regent). He based his power on the richer cossacks ('starshina') and sought a rapprochement with Poland. This led to a rebellion of the more democratic cossacks Martyn Pushkar and Yakiv Barabash, which was defeated in June 1658, a civil war that cost about 50,000 lives. In September 1658 he signed the Treaty of Hadiach with Poland, which would have turned Ukraine into a third member of the Polish–Lithuanian commonwealth, but the treaty was never implemented. The treaty led to a massive Russian invasion that was defeated at the Battle of Konotop on 29 June 1659. Faced with a revolt by several pro-Moscow colonels, Vyhovsky resigned and retired to Poland in October 1659.