How did Jewish defense organizations such as the Haganah develop before 1948?

The Haganah (Hebrew for "Defense") was established in 1920 as a Zionist military organization to protect Jewish settlements in Palestine against revolts by Palestinian Arabs.1

Early development was characterized by the following:

• Organizational Structure: It operated under the influence of the Histadrut and functioned primarily with a part-time membership.1
• Policy of Restraint: For much of its existence, the Haganah adhered to havlaga ("self-restraint"), maintaining a moderate stance that explicitly rejected the terrorist tactics employed by groups like the Irgun Zvai Leumi and the Stern Gang.1
• Expansion: In 1941, the organization formed the Palmach, a full-time commando force.1
• Shift in Strategy: Following World War II, the Haganah abandoned its policy of restraint and engaged in sabotage against British infrastructure to protest restrictions on Jewish immigration.1

By 1948, the Haganah transitioned from an underground, outlawed militia into the official national army of the newly established State of Israel, eventually becoming the Israel Defense Forces.1