Nation building through unification versus secession

From The Long Shadow: The Legacies of the Great War in the Twentieth Century by David Reynolds.  Page 12.

Whether peaceful or violent, this new spasm of European state building after 1918 was different from that of the mid-nineteenth century. Whereas Italy and Germany had been created through the unification of various local polities with similar language and culture, state building in eastern and southeastern Europe occurred through secession from dynastic empires that had hitherto controlled a volatile mix of ethnic groups in various stages of national self-consciousness and political mobilization. In the vanguard were shrewd nationalist politicians like Masaryk and Piłsudski, who harked back to an ancestral kingdom as the core of the new state. But because of the process of secession and fragmentation, they had to use what they could get from the imperial rubble heap, and their jerry-built new states were a mix of various ethnic groups who had previously lived cheek by jowl. Not so much nation-states as mini empires, with the ethnic tensions of prewar now exacerbated by four years of brutal fighting. A process of state building and national mobilization that had taken decades, even centuries, in Western Europe occurred almost overnight from the Baltic to the Adriatic, often with horrific violence.