Could Ivan IV, tsar of Russia, somehow be elected king of Poland and grand Duke of Lithuania after Sigismund II's death in 1572? Assuming the answer is yes, could such an union spark a war in Eastern Europe? I doubt states like Sweden, the Habsburg dominions and the Ottoman Empire would like having a giant new empire that stretches from Warsaw to Kazan sitting right at their doorstep. Plus, what would be Ivan's relations with the szlachta? Probably terrible, given his autocratic nature.