Why was "tantrum" trending last week?
1844, "devotion to one's country;" see nationalist + -ism; in some usages from French nationalisme. Earlier it was used in a theological sense of "the doctrine of divine election of nations" (1836). Later it was used in a sense of "doctrine advocating nationalization of a country's industry" (1892).
The strong belief that the interests of a particular nation-state are of primary importance. Also, the belief that a people who share a common language, history, and culture should constitute an independent nation, free of foreign domination.
Note: Nationalism is opposed to colonialism and imperialism.