The Irgun was an offshoot of the Haganah, the more defensive paramilitary force organized in 1920 to protect Jewish settlers. Irgun members disagreed with the Hanaga’s relatively less confrontational posture toward Palestinian Arabs and British authorities.
Irgun’s activities in the late 1930s and 1940s included terrorist raids on civilian population centers such as markets, bus stations, hotels and pedestrian areas. The group's most lethal fuse was lit when Britain's Peel Commission concluded that the best solution to the Jewish-Palestinian problem in Palestine was partition, an option Irgun would not abide.
Based on Zionist Revisionism founder Zeev Jabotinsky’s ideology, the Irgun rejected all notions of partitioning Palestine or sharing it with Palestinians or Arabs. Irgun believed in an exclusively Jewish, national state that would claim all of Palestine and Trans-Jordan (present-day Jordan), South Lebanon up to the Litani River, the Gaza Strip and parts of the Sinai Peninsula.
To populate Palestine fast and in spite of British immigration restrictions, Irgun developed an illegal-immigration underground from Eastern Europe, particularly from Poland.
The band’s most notorious terrorist acts were the massacre of Palestinian civilians at the village of Deir Yassin in 1948, where up to 130 Palestinians, most of them women, children or old people, were murdered, and the 1946 bombing of the King David Hotel in Jerusalem, where British authorities were headquartered. Ninety-one people were killed in that attack. Both attacks were organized by Begin.
Irgun’s terror campaign was designed in part as retribution for Arab attacks on Jews and in part as a method of frightening Arabs away from their properties and tenements. The Deir Yassin massacre had that desired effect.
By the late 1940s, even Winston Churchill was telling the British Parliament that Britain’s Mandate over Palestine safeguarded “no British interest, leading the Cabinet to decide ion Feb. 14, 1947 to dump the “Palestine problem” into the United Nations’ lap. According to historian Michael Cohen (writing in Palestine and the Great Powers, 1945-1948, Princeton, 1982), “the IZL’s draconian methods, morally reprehensible as they were, were decisive in transforming the evacuation option of February 1947 into a determined resolve to give up the burden of the Mandate.”
On June 1, 1948, Begin signed an agreement with Israel’s new military force to fold Irgun members into what became known as the Israel Defense Forces.