Final answer:
Greece initiated a revolt against Turkish rule during Alexander the First's reign, known as the Greek War of Independence starting in 1821, supported by powerful European countries.
Step-by-step explanation:
The country that revolted against Turkish rule during Alexander the First's reign was Greece. This revolt is known as the Greek War of Independence, which started in 1821. It was part of the broader context of the decline of the Ottoman Empire and the rise of nationalism within its territories. Alexander Ypsilantis, a Greek prince, sparked the rebellion that resonated with the Greeks' desire for autonomy and recognition as an independent, self-governing nation. Notably, the European powers, including Imperial Russia, Britain, and France, provided support to the Greeks in their struggle against Ottoman rule. This support was partly influenced by the Romantic movement in Europe and the symbolic significance of Greece as the birthplace of democracy and classical civilization.