: loyalty and devotion to a nation; especially : a sense of national consciousness (see consciousness 1c) exalting one nation above all others and placing primary emphasis on promotion of its culture and interests as opposed to those of other nations or supranational groups <Intense nationalism was one of the causes of the war.>https://www.merriam-webster.com/dictionary/nationalism
And according to dictionary.com
spirit or aspirations common to the whole of a nation.
devotion and loyalty to one's own country; patriotism.
excessive patriotism; chauvinism.
the desire for national advancement or political independence.
the policy or doctrine of asserting the interests of one's own nation viewed as separate from the interests of other nations or the common interests of all nations.
an idiom or trait peculiar to a nation.
a movement, as in the arts, based upon the folk idioms, history, aspirations, etc., of a nation.