Article: Pan-Slavism, a movement which came into prominence in the mid-19th century, emphasized the common heritage and unity of all the Slavic peoples. The main focus was in the Balkans where the South Slavs had been ruled for centuries by other empires: the Byzantine Empire, Austria-Hungary, the Ottoman Empire, and Venice. The Russian Empire used Pan-Slavism as a political tool; as did the Soviet Union, which gained political-military influence and control over most Slavic-majority nations between 1945 and 1948 and retained a hegemonic role until the period 1989–1991.

Question: How long did the Soviet Union retain a hegemonic role?
until the period 1989–1991