Final answer:
The Austro-Hungarian Empire controlled much of Eastern Europe before World War 1, while the Ottoman Empire, known as the 'Sick Man of Europe', was in decline and lost most of its European territories.
Step-by-step explanation:
The empire that controlled much of Eastern Europe before World War 1 was the Austro-Hungarian Empire. This empire, along with the Ottoman Empire and the Russian Empire, was one of the great powers of Europe and played a significant role in the politics of the region. By the eve of World War 1, the Austro-Hungarian Empire had taken control of Bosnia and Herzegovina, but the region was riddled with nationalist tensions among Slavic populations who sought independence or unification with Serbia. These tensions were compounded by international rivalries and alliances involving major European powers, turning the Balkans into a volatile hotspot that would trigger the outbreak of the Great War.
The Ottoman Empire, also known as the 'Sick Man of Europe', was declining in strength throughout the 19th century and lost most of its European territories after the Balkan Wars. By aligning with Germany in World War 1, the Ottoman Empire sought to reclaim lost territories and prestige, but the war ultimately hastened the end of both the Ottoman and Austro-Hungarian empires.