Soon after the end of World War II, there were three basic para-military Zionist organizations in Palestine, working against the Arab people, with the specific purpose of driving it out of Palestine. These were the Haganah, the Irgun Zvai Leumi and the Stern Gang.
Before the British Mandate, the Jewish settlers had formed a group of mounted armed watchmen called "Hashomar" and with the advent of the British Mandate, it became the Haganah (Defense). With a membership of 60,000 Zionist Jews, the Haganah had a field army of 16,000 trained men and a unit called the Palmach, which was a full-time force, numbering about 6000.
The Irgun Zvai Leumi included between 3000 and 5000 armed terrorists, and grew out of the Haganah and its Palmach branch in 1933. The Irgun was not ready to obey the Jewish Agency which sought to dilute the terror of the Haganah in order not to lose its respectability.
In 1939, one of Irgun's commanding officers, Abraham Stern, left the parent organization and formed the Stern Gang, numbering some 200 to 300 dangerous fanatics.
