Explanation:

In Eastern Europe, after World War I, the greatest obstacle to national unity in many nation states was the Great ethnic diversity found in the region. The First World War destroyed empires, created numerous new nation-states, encouraged independence movements in Europe’s colonies, forced the United States to become a world power and led directly to Soviet communism and the rise of Hitler. Diplomatic alliances and promises made during the First World War, especially in the Middle East, also came back to haunt Europeans a century later.