AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
Option A — Both A and R are true, and R is the correct explanation of A. The Balkans was the most serious source of nationalist tension after 1871 precisely because of its ethnic and geographical diversity, and its peoples used nationality and history of subjugation to claim independence.
Source: Nationalism and Imperialism, Chapter 1
The textbook directly states the Balkans was "the most serious source of nationalist tension in Europe after 1871" and that its peoples "based their claims for independence on nationality" and history of foreign subjugation — making R the direct cause of A. So both statements are true and R correctly explains A.