A key factor of the empires the United States and European countries built in the late 1800s was:

Nationalism—the belief that one’s nation is important and should be powerful—helped motivate the United States and European countries to build empires in the late 1800s. Acquiring colonies was seen as a way to increase national prestige and influence. Chauvinism means exaggerated or aggressive patriotism, but the broader key factor named here is nationalism.

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