The largest nation before the First World War was Austria-Hungary. Poland was divided up among Austria-Hungary, Prussia, and Russia.
Europe before the First World War (1871 – 1914)
World War I began in the Balkans and occurred between July 1914 and November 11, 1918. By the end of the war, over 20 million people would be killed.
After World War I four empires collapsed ( The German Empire, the Austro-Hungarian Empire, the Ottoman Empire, Russian Empire). The collapse of these empires led to the formation of multiple new countries, the most important of which included Poland, Yugoslavia and and Czechoslovakia. Other European countries like France, Italy, and Romania increased in size.
Europe during the Interwar period (1919 – 1939)