History. 20th century

During the 19th century, European powers expanded into the world in an unprecedented manner. During the 20th century, the same powers turned in on themselves to produce one of the bloodiest periods in human history.   What were the economic, political, and cultural motives behind 19th-century European imperialist expansion?   How did European imperialism, colonialism, and nationalism anticipate the coming of the Great War?   What role did economic and political instability after the Great War play in the coming of the Second World War?   Finally, how and why did the experiences of World War II lead to the processes of decolonization and the rise of nationalism during the post-war period?