Nationalistic and ethnic tensions prior to World War I created the “Powder Keg of Europe.” This name was given to the

Balkans.

Explanation:

After Congress of Berlin there were many independent states created on the Balkan Peninsula. Still, some great forces, especially Austria-Hungary wanted to gain more influence. The things really heated up in 1908 when Austria-Hungary annexed Bosnia and Herzegovina. Together with the Balkan Wars this was one of the causes of WW1.

would not cooperate with each other voluntarily.

i think it is the byzantine empire