Updated: May 5, 2021
Before the establishment of the State of Israel, there were various paramilitary organizations that eventually banded together to form what we now know as the Israel Defense Forces.
The Haganah was founded following the Palestine Riots of 1920. These events made the leaders of the Yishuv (the Jewish community in British Mandate Palestine) realize the need for a nationwide paramilitary organization. The Haganah progressively became a full-fledged military force as the need grew over the years. After the establishment of Israel the Haganah, along with the other military organizations of the time, banded together to form the IDF.
The Irgun was a paramilitary organization that operated in British Mandate Palestine between 1931-1948. It was an offshoot of the Haganah and for a period of time after the split was referred to as the Haganah Bet. The Irgun was based on Revisionist Zionistic principles, following the leadership of Zeev Jabotinsky. The Irgun fought for the right that every Jew had the right to enter Palestine, the only active force would prevent rioting and attack, and only a Jewish military would ensure the establishment of a Jewish state. The Irgun, led at the time by Menachem Begin, is well known for bombing the King David Hotel, where British personnel was headquartered.
The Lehi was a paramilitary organization operated in British Mandate Palestine. Their main goals were to evict the British from Palestine by force, create unrestricted Jewish immigration, and establish a Jewish state. The organization was organized by Avraham Stern, and as a result, the Lehi was often referred to as the Stern Gang. The Lehi was originally part of the Irgun, but they split from them during World War II, so that the Lehi soldiers could continue to fight the British. They felt there was a conflict after the Irgun agreed to fight for the British during World War II in the Jewish Brigade.
The Palmah was the elite fighting force of the Haganah. By 1948 the Palmah consisted of over 2,000 men and women. The Palmah consisted of three branches, all of which were disbanded in 1948 after the establishment of the State of Israel. The members of the Palmah greatly contributed to the backbone of Israeli society, as many of the future military and political leaders had been a member of the Palmah. Some of the notable Palmachniks included Moshe Dayan and Yitzhak Rabin.