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

totalitarianism.

patriotism.

chauvinism.

nationalism.

Nationalism.

Explanation:

Nationalism, as a political idea, is the ideology to maintain the self-governance of the country and to protect its borders against foreign interference. Another vision about this conception is the love for the country, and to promote an identity (political and social). The first half of the 19th century was marked by the dissolution of the Absolute monarchies and the development of the National State. The nationalist movement evolved in many ways during the 19th century. In countries such as France and the United States, institutions such as schools, political parties, trade unions, and the army played a relevant role in the development of nationalism, as well as the construction of national symbols, such as literature and its histories.