What exactly is nationalism and why did it grow as much as it did in the 19th century?

Nationalism is the belief of extreme patriotism and heavy independence. Throughout the 19th century ideals like 100% American took hold in American society. Enormous influxes in immigration fed the passion for these beliefs.

Nationalism is an immense sense of pride in one’s nation of culture, usually leading to widespread movements of independence, protest, etc.

In the 19th century, a lot of things went on at once. Many nationalists were influenced by Enlightenment thinkers such as Voltaire’s tolerance and John Locke’s natural rights. People had gotten tired of the abuses of the government and, influenced by the Enlightenment, banded together to gain independence.

Also, as empires such as the British and Ottoman were expanding, they conquered vastly different cultures and people. As time went on, these people didn’t want to be associated with a collective group of ethnicities they couldn’t truly relate to; this resulted in ethnic movements of independence where they sought to form their own nations. Examples include the unification of Italy and the unification of the Germanic-speaking peoples into Germany.