Final answer:
Russia was the country that evolved from the Principality of Vladimir-Suzdal to the Tsardom of Muscovy and became an Empire in 1721. Under the rule of Ivan the Great and his grandson Ivan the Terrible, Russia began its expansion, which continued under various rulers, including Catherine the Great, until it became an immense empire with a diverse population.
Step-by-step explanation:
The country that was initially independent under the Principality of Vladimir-Suzdal, which later became the Tsardom of Muscovy, and eventually transformed into an Empire in 1721 is Russia. The Russian Empire's roots can be traced back to the Grand Duchy of Moscow led by Ivan III, also known as Ivan the Great, who refused to pay tribute to the Golden Horde. His grandson, Ivan IV (Ivan the Terrible), was the first to take on the title Tsar of all the Russias - a title equating to "Caesar". Under his reign, territories such as the Khanates of Kazan, Astrakhan, and Siberia were annexed, and colonization of Siberia was initiated.
Later on, under the rule of Catherine the Great during the 18th century, the Russian Empire expanded significantly to include areas like Ukraine and the northern Caucasus Mountains. This expansion continued into the 19th century, adding territories from Central Asia to parts of Eastern Europe. However, within its borders, the Russian Empire faced internal challenges like resistance to serfdom, demand for reforms, and political unrest which eventually led to revolutions and the rise of the Soviet Union in the 20th century.