This aliyah, a continuation of the Second Aliyah (which was interrupted by World War I), was triggered by the October Revolution in Russia, the ensuing pogroms there and in Poland and Hungary, the British conquest of Palestine and the Balfour Declaration. Most members of the Third Aliyah were young halutzim (pioneers) from Eastern Europe. Although the British Mandatory regime imposed aliyah quotas, the yishuv numbered 90,000 by the end of this period. The new immigrants built roads and towns, and projects such as the draining of marshes in the Jezreel Valley and the Hefer Plain were undertaken. The General Federation of Labor (Histadrut) was established, representative institutions for the yishuv were founded (the Elected Assembly and the National Council), and the Haganah (the clandestine Jewish defense organization) was formed. Agricultural settlement expanded, and the first industrial enterprises were established.
Approximately 40,000 Jews arrived in Palestine during the Third Aliyah; relatively few returned to their countries of origin.