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His greatest achievements outside the field of the sociology of the Jews were in that of settlement. Ruppin's work can be divided into four periods: in the first (1908–14) he laid the foundations for Zionist settlement; in the second (1914–18) he participated in the struggle to save the yishuv from destruction; in the third (1920–33) he took part in the systematic expansion of settlement in the cities and rural areas and of the country's economy, throughout political and economic crises; and in the last period (1933–42), when he was a recognized expert on the economy of the country and the sociology of the Jews, he filled a central role in the absorption of the Fifth Aliyah, which brought tens of thousands of immigrants from Germany and refugees from Nazi-occupied Europe, and in solving the problems that resulted from their migration.