Ultimately the island of Hortica, just below the falls of the Dnieper, was fixed upon as their headquarters; and on the numerous islands of that broad river there gradually arose the famous Cossack community known as the Zaporozhskaya Syech, or Settlement behind the Falls, whence the Dnieperian Cossacks were known, generally, as Zaporozhians, or Backfallsmen.
proposed to make the Cossacks the pivot of his foreign policy and his domestic reforms. His far-reaching plans were based upon two facts, the absolute devotion of the Zaporozhians to himself personally, and the knowledge, secretly conveyed to him by Stanislaus Koniecpolski, that the whole of the Ukraine was in a ferment.
On the 18th of April 1648, at the general assembly of the Zaporozhians, he openly expressed his intention of proceeding against the Poles and was elected hetman by acclamation; on the Toth of May he annihilated a small detached Polish corps on the banks of the river Zheltndya Vodui, and seven days later overwhelmed the army of the Polish grand-hetman, massacring 850o of his 10,000 men and sending the grand-hetman himself and all his officers in chains to the Crimea.
newly elected king of Poland, John Casimir, Wladislaus IV.'s brother, privately opened negotiations with the rebel, officially recognized him by sending him the bulawa and the other insignia of the hetman's dignity, and promised his "faithful Zaporozhians" the restoration of all their ancient liberties if they would break off their alliance with the Tatars and await the arrival of peace commissioners at Pereyaslavl.
By the compact of Zborow (Aug 21, 1649) Chmielnicki was recognized as hetman of the Zaporozhians, whose registered number was now raised from 6000 to 40,000; a general amnesty was also granted, and it was agreed that all official dignities in the Orthodox palatinates of Lithuania should henceforth be held solely by the Orthodox gentry.
On the I Ith of April 1648, at an assembly of the Zaporozhians (see Poland: History), he openly declared his intention of proceeding against the Poles, and was elected ataman by acclamation.