The Irgun Tsvai Leumi, the Hebrew name for the National Military Organization, was formed in 1931 after it split from the Haganah Zionist organization under the leadership of Abraham Tehomi. This military group is attributed to many of the tragedies and massacres against the Palestinian people. Its emblem featured a map of Palestine and Jordan with a rifle, surrounded by the Hebrew text "Rak Kach" meaning "Only Thus."
One of the primary reasons for the Irgun's breakaway from the Haganah was their dissatisfaction with the British-imposed restrictions on dealing with Palestinian rebels. They openly disregarded Arabs, advocated for the historic land of Israel on both sides of the river (all of Palestine and East Jordan). Prominent leaders included Israel's Prime Minister Menachem Begin and Isaac Shamir before Shamir joined Stern in 1940.
The Irgun was considered the most powerful Zionist organization during that period, not just due to its size but also because of the numerous terrorist operations it carried out against the Palestinian people and British mandate authorities. It was later classified as a terrorist organization, alongside the Stern Gang. The organization committed dozens of crimes against the Palestinian people from its inception until its dissolution in 1948, forming, alongside other Zionist military organizations, the nucleus of the Israeli Defense Forces. The Deir Yassin massacre on April 9, 1948, conducted in collaboration with the Stern Gang, was among its most heinous crimes, resulting in the deaths of over 245 Palestinian civilians.
The group also targeted British military personnel, as evidenced by the bombing of the administrative headquarters of the British Civil Administration in the King David Hotel in Jerusalem on July 22, 1946.