Why did nationalism spread throughout Europe during the Napoleonic era?

Nationalism spread throughout Europe during the Napoleonic era primarily due to the impact of the French Revolution and Napoleon's conquests. The revolutionary ideals of liberty, equality, and fraternity inspired various ethnic groups to seek self-determination and assert their national identities. Additionally, Napoleon's establishment of the Napoleonic Code and his military campaigns often dismantled old feudal structures, fostering a sense of national unity and pride among diverse populations. This era also sparked resistance against foreign domination, further fueling nationalist sentiments across the continent.