Editing Bohdan Khmelnytsky (section)

===Complications===
[[File:Bohdan-banner.jpg|thumb|Bohdan Khmelnytsky's banner that was taken at the [[battle of Berestechko]]. It was later taken by the Swedes in Warsaw 1655 and is now to be seen at Armémuseum, [[Stockholm|Stockholm, Sweden]].]]
Khmelnytsky's initial successes were followed by a series of setbacks as neither Khmelnytsky nor the Commonwealth had enough strength to stabilise the situation or to inflict a defeat on the enemy. What followed was a period of intermittent warfare and several peace treaties, which were seldom upheld. From spring 1649 onward, the situation turned for the worse for the Cossacks; as Polish attacks increased in frequency, they became more successful. The resulting [[Treaty of Zboriv]] on 18 August 1649 was unfavourable for the Cossacks. It was followed by another defeat at the [[battle of Berestechko]] on 18 June 1651 in which the Tatars betrayed Khmelnytsky and held the hetman captive. The Cossacks suffered a crushing defeat, with an estimated 30,000 casualties. They were forced to sign the [[Treaty of Bila Tserkva]], which favoured the Polish-Lithuanian Commonwealth. Warfare broke open again and, in the years that followed, the two sides were almost perpetually at war. Now, the [[Crimean Tatars]] played a decisive role and did not allow either side to prevail. It was in their interests to keep both Ukraine and the Polish–Lithuanian Commonwealth from getting too strong and becoming an effective power in the region.<ref name = "Subtelny">[[Orest Subtelny]]. ''Ukraine. A history.'' University of Toronto Press, p. 133. 1994. {{ISBN|0-8020-0591-8}}.</ref>

Khmelnytsky started looking for another foreign ally. Although the Cossacks had established their ''[[de facto]]'' independence from Poland, the new state needed legitimacy, which could be provided by a foreign monarch. In search of a protectorate, Khmelnytsky approached the [[Ottoman sultan]] in 1651, and formal embassies were exchanged. The Turks offered vassalship, like their other arrangements with contemporary [[Khanate of Crimea|Crimea]], [[Moldavia]] and [[Wallachia]]. However, the idea of a union with the Muslim monarch was not acceptable to the general populace and most Cossacks.

The other possible ally was the [[Tsardom of Russia]]. However, despite appeals for help from Khmelnytsky in the name of the shared Orthodox faith, the tsar preferred to wait, until the threat of a Cossack-Ottoman union in 1653 finally forced him to action.<ref name = "Subtelny" /> The idea that the tsar might be favourable to taking Ukraine under his hand was communicated to the hetman and so diplomatic activity intensified.