Final answer:
The Ottoman Empire primarily reigned in what is now modern-day Turkey, experiencing great expansion at its peak and decline by the 19th century, ultimately dissolving after World War I.
Step-by-step explanation:
The Ottoman Empire was a vast and influential empire that reigned primarily in what is now modern-day Turkey. It was at the crossroads of Europe, Asia, and Africa, ruling over a population diverse in ethnicity, language, and religion. The empire started in the late thirteenth century and persisted until World War I, going through periods of great expansion and eventual decline. At its peak in the 16th century, under Sultan Suleiman I, the Ottoman military was a dominant force in the Mediterranean world. It expanded into Southeast Europe, North Africa, the Middle East, and even made forays into the Indian Ocean region. However, by the 19th century, referred to as "the Sick Man of Europe," it experienced a slow decline, leading up to its dissolution in the aftermath of World War I, after which Turkey emerged as its successor state.