Irgun, in addition to its terrorist activities, participates also in the organization of illegal immigration into Palestine after the publication of the 1939 White Paper.

Irgun's violent activities lead to execution of many of its members by the British; in retaliation, Irgun executes British army hostages.

After a policy split in Irgun in 1940, thirty-three-year-old Avraham Stern founds a small terrorist splinter group, LEHI, formally Lohame Herut Yisra'el (Hebrew: "Fighters for the Freedom of Israel"), also known as the Stern Gang, or Stern Group, after its founder.

Another of its founding members,  twenty-five-year-old Yitzhak Shamir, had joined the Betar Zionist youth movement as a young man and studied law in Warsaw.

He had emigrated to Palestine in 1935 and enrolled at the Hebrew University in Jerusalem, where he had joined Irgun.