How did new ideas about national identities change the balance of power in the world???

National identity and the conflicts that arise from this concept have historically been the main factor of change in the geopolitical balance of power worldwide.

Throughout history and even in the contemporary era, many nations have changed their borders, gained or lost resources, or even ceased to exist as a consequence of changes in the national identity of their inhabitants.

Thus, the separation of Austria-Hungary into two independent nations in 1918 led to the disappearance of one of the main economic and political powers on the continent; the dissolution of the Soviet Union in new independent nations ended with the bipolarity of the Cold War; the feeling of German unity that unified East Germany and West Germany gave way to a new power in Europe in 1990; and the Russian patriotic sentiment in the Ukrainian region of Crimea gave way to a bilateral conflict that ended with the annexation of this region by Russia.

i think it is the byzantine empire

the answer to number 5 is fort sumter