Hostilities were initiated in 627 AD by Khagan Tong Yabghu of the Western Göktürks and Emperor Heraclius of the Eastern Roman Empire. Opposing them were the Sassanid Persians, allied with the Avars. The war was fought against the background of the last Byzantine-Sassanid War and served as a prelude to the dramatic events that changed the balance of powers in the Middle East for centuries to come (Battle of Nineveh, Islamic conquest of Persia).