Between 1914 and 1922, millions of Europeans left their homes as a result of war, postwar settlements, and revolution. After 1918, the immense movement of people across Germany's eastern border posed a sharp challenge to the new Weimar Republic. Ethnic Germans flooded over the border from the new Polish state, Russian émigrés poured into the German capital, and East European Jews sought protection in Germany from the upheaval in their homelands...