The southernmost territories of the Commonwealth were inhabited by a large population of Zaporozhian Cossacks — a free folk whose legal status was partly regulated. In danger of being invaded by Crimean Tatars, they lived in constant military readiness, which made them excellent soldiers. The entire 16th century and the first half of the 17th century were abundant in examples of their brave defense of the Commonwealth. At the same time they often raided Turkish lands, thus provoking diplomatic crises between Warsaw and Istanbul. The Commonwealth tried to discipline them by registering some of them as soldiers (the Cossack Register) or turning them into serfs.
Consequently, the Cossacks regularly rebelled for the purpose of expanding the register and obtaining a guarantee of their rights, which would have protected them from having the peasant status imposed on them. The greatest of the rebellions took place in 1648, led by Bohdan Khmelnytsky. The weakened Commonwealth found itself unable to oppose it. A few compromising military defeats resulted in the rebels’ strengthening on the south-eastern lands, of which Warsaw lost control. The war, which was dragging on and which neither side was able to settle in its favor, ruined the Ukrainian lands and also put a heavy economic burden on the Commonwealth’s shoulders. The Cossacks also dragged Moscow into the conflict, subjecting Ukraine to the tsar.
When Ivan Vyhovsky became the Hetman of the rebellion, supporters of an agreement with the Poles prevailed among the Cossacks. The willingness to end the destructive war was dominant also on the Polish side. In consequence, in 1658, the Treaty of Hadiach was signed. It transformed the Polish-Lithuanian Commonwealth into a Commonwealth of Three Nations, granting a separate status to the territories inhabited by Cossacks. It guaranteed the Orthodox population’s rights and also the Cossacks’ gradual ennoblement. A separate ladder was created for offices on the Ukrainian lands, which were to be held only by individuals originating from those territories. The nobility could return to its landed estates.
The controversy whether the Treaty of Hadiach could put an end to the destructive civil war continues. Shortly after its signing, rank-and-file Cossacks rebelled against Vyhovsky under Moscow’s influence. Vyhovsky was then deprived of the mantle of Hetman and the war against the Commonwealth resumed.
