https://en.wikipedia.org/wiki/Pan-Slavism
Pan-Slavism, a movement which crystallized in the mid-19th century, is the political ideology concerned with the advancement of integrity and unity for the Slavic peoples.Its main impact occurred in the Balkans, where non-Slavic empires had ruled the South Slavs for centuries. These were mainly the Byzantine Empire, Austria-Hungary, the Ottoman Empire, and Venice