How did the idea of nationalism lead to nation building in Europe in the 19th Century?

Nationalism was the ideological driving force behind nation-building in the nineteenth century. A shared sense of identity with other "Germans" and "Italians," for example, helped to build popular support for the unification of these countries--Italy, as one European leader said, was nothing more than a "geographic expression" before the 1860s. (I focus here on these two nations because nation-building there served as an example for other nations). As early as the 1810s, nationalistic organizations like Giuseppe Mazzini's "Young Italy" emerged, creating momentum for the formation of nation-states. As historian Benedict Anderson has shown, the spread of print media also facilitated nationalism by helping to create a shared culture, or an "imagined community" as Anderson called it. The actual mechanics of nation-building was carried out by statesmen such as Count Cavour in Italy and Otto von Bismarck in Germany, and the liberal ideals that often accompanied nationalistic sentiment in Europe were largely absent from the governments formed by these men. But nationalism played a pivotal role in mobilizing popular support for forming nation-states in Italy and Germany.