The First Aliyah (1882-1903) was largely instigated by pogroms in Russia in the late 19th century as well as some Jews interested in building a Jewish community in Palestine. Nearly 25,000 Jews came to Palestine during this time. 2
The Second Aliyah (1904-1914) began a few years after Theodor Herzl founded the Zionist movement, and amidst growing antisemitism and economic hardship in Eastern Europe. Many future Zionist leaders, including David Ben-Gurion, arrived in this wave and the first kibbutzim (קיבוצים) were founded. The Second Aliyah brought 35,000 immigrants, though many left due to the difficult living conditions they encountered.
Most members of the Third Aliyah (1919-1923) were young chalutzim (חלוצים), or pioneers, from Eastern Europe who left in the aftermath of the 1917 Russian Revolution. During this time, agricultural projects expanded rapidly and the Haganah—the primary pre-State fighting force and the predecessor of the IDF—was founded. About 40,000 immigrants came as part of this wave.
The Fourth Aliyah (1924-1929) came about due to continued economic crises and antisemitism in Eastern Europe, as well as stiff immigration restrictions elsewhere. Another 80,000 Jews immigrated during this wave.
The Fifth Aliyah (1929-1939) was fueled by the rise of the Third Reich in Germany. Some 250,000 Jews arrived as part of this wave.
Aliyah Bet (1920-1948) refers to the illegal immigration of Jews to Palestine. In the era of the British Mandate, particularly after 1939, the British limited the immigration of Jews, leading Zionist organizations to smuggle Jews into Palestine covertly. Over 100,000 Jews, some of whom were caught and detained in Cyprus, arrived through these illegal channels.