Romantic nationalism was an integral part of actual nationalist political movements, movements that emerged in earnest in the immediate aftermath of the Napoleonic wars. Those movements would ultimately succeed in seeing their goals realized almost without exception, although that process took over a century in some cases (like those of Poland and Ireland). Central to nationalist movements was the concept that the state should correspond to the identity of a “people,” although who or what defines the identity of “the people” proved a vexing issue on many occasions.
The discussion of nationalism starts with the French Revolution, because more than any other event, it provided the model for all subsequent nationalisms. The French revolutionaries declared from the outset that they represented the whole "nation," not just a certain part of it. They erased the legal privileges of some (the nobles) over others, they made religion subservient to a secular government, and when threatened by the conservative powers of Europe, they called the whole "nation" to arms. The revolutionary armies sang a national anthem, the Marseillaise, whose lyrics are as warlike as the American equivalent. Central to French national identity in the revolutionary period was fighting for la patrie, the fatherland, in place of the old allegiance to king and church.
The irony of the French revolutionary and Napoleonic wars, however, was that the countries invaded by the French eventually adopted their own nationalist beliefs. The invaded countries turned the democratic French principle of self-determination into a sacred right to defend their own national identities, shaped by their own particular histories, against the universalist pretensions of the French. That was reflected in the Spanish revolt that began in 1808, the revival of Austria and Prussia and their struggles of "liberation" against Napoleon, Russia's leadership of the anti-Napoleonic coalition that followed, and fierce British pride in their defiance to French military pretensions.