The other possible ally was the Orthodox tsar of Moskovia. That government remained quite cautious and stayed away from the hostilities in Ukraine. In spite of numerous envoys and calls 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. The idea that the tsar might be favourable to taking Ukraine under his hand was communicated to the hetman and so diplomatic activity intensified.