Final answer:
The mid-19th century adoption of national anthems in Europe symbolized the growth of nationalism and the rise of national identities, leading to unification and aggressive colonial expansion.
Step-by-step explanation:
The adoption of national anthems by European countries in the mid-19th century marked a period of growing nationalism and the emergence of national identity. Nationalistic sentiments grew particularly after the Napoleonic wars, as seen in Germany with the nationalist gatherings and identification with the black, red, and gold tricolor flag. The latter part of the 19th century was characterized by political transformations, economic industrialization, colonial expansion, and cultural identity struggles within European nations, building towards the unification of Italy and Germany. Aggressive nationalism emerged towards the end of the century, leading to a new focus on colonial expansion into Africa following the expeditions and settlements that brought about significant economic opportunities for European powers.