How did nationalism change the balance of power in Europe.?

Nationalism significantly altered the balance of power in Europe by fostering a sense of unity among people with shared cultural, linguistic, or historical identities, often leading to the formation of nation-states. This shift weakened multi-ethnic empires, such as the Austro-Hungarian and Ottoman Empires, as nationalist movements sought independence or greater autonomy. Additionally, it heightened tensions between established nations, as rival nationalist sentiments led to competition and conflict, contributing to events like World War I. Ultimately, nationalism reshaped alliances and rivalries, influencing the geopolitical landscape of Europe.