The late nineteenth century was a time of high nationalism, particularly in Europe. German unification took place in 1871, as did the Italian Risorgimento. Even in nation-states which had been unified for much longer, such as France, there was an intensification of national feeling as centralized states began to assert monopolies of force and control over specific territories. Where people might have tended to identify on a more local level, governments began to encourage identification nationally instead. Sometimes this included explicit patronage of artists, who the state employed to create symbols of the nation-state. One example of this with which I am familiar is Emanuel Gottlieb Leutze's Westward the Course of Empire Takes its Way, commissioned for the United States Capitol. Throughout the 1860s and 1870s there were a series of commissions for the Capitol, intended to tell the cultural story of the United States at the center of its government. This undoubtedly happened in Europe, as well, though I am less familiar with specific examples.

If you are interested in the rise of nationalism more generally, a foundational text in the area is Benedict Anderson's Imagined Communities, in which he explores the ways in which a nation is imagined, rather than the result of practical and everyday interactions between citizens.