While the two Empires were facing Confronting_problem enormous internal difficulties , the Serbs took Creating the favorable opportunity to expand Expansion its domain .

By 642 AD , under Caliph Umar , Arab Muslim forces had laid Placing control Control of Mesopotamia ( 638 ) , Syria ( 641 ) , Egypt ( 642 ) , and had invaded Attack Armenia , all previously territories split Motion between the warring Hostile_encounter Byzantine and Persian Empires , and were concluding Process_end their conquest Conquering of the Persian Empire with their defeat Conquering of the Persian army at the Battle Hostile_encounter of Nahāvand .

In the late 1550s , the ruler of one of the Kabardás , Temryuk ( or Temriuk ) , struck Attack a politico-military alliance with Tsar Ivan IV of Russia ( `` Ivan the Terrible '' ) , for mutual assistance against expansionist attacks Attack by the Persian and Ottoman Empires .