Well, if i may explain this in a vey long post, that is partially historic.
All through our History, Jews have suffered some sort of violence from other nations and people. The Parsians, the Greeks, and the Romans were among theones to conqure us in the ancient times. Though the Jews were never fearsome warriors, we have had a few examples of military tredtion. Among these you may find King David, the Maccabis, and Bar Kochva. The Maccabis fought and defeated the Greeks, and Bar Kochva fought a short and bloody wr against the Romans, which ended in most Jews being kicked out of the land of Israel. The Jews spent the next 2000 years in Europe. There they suffered from Pogroms and other violence. But they did not defend them selves. They were merchents and religious men, not soldiers. Only in the late 19 Century did Jews start to join Europian and other armies, and even then in small noumbers. It can be said then that until the 20th century, Jews were not really warriors.
It was WWI that saw the first Jewish units in European Armys. There were a few Jewish Regiments in the British Army. There were also many Jews who fought for Austro-Hungary, and Germany. The Jews that served in the British Army were mostly pioneers from Eretz Israel/Palestine. When they came back from the war, to the reality of hostilities with the local Arabs, the Jews in Palestine saw that they must form some sort of defence organization. In the 1930 this happend, and "Hagana"(Hebrew for Defense) was formed. This organization was clandestine(the British who ruled palestine did not want the Jews to arm them selves), and was meant mostly to secure Jewish towns and escort convoys. The members were normal people from the comunity, who were given basic training in squad based warfare. The best unit in the Hagana, and basically its "Commando", was the PALMACH- short for Plugot Machatz- Assault Companies. These were very motivated, well ttrained men and women, who were used in operations against the Brits and the Arabs.
In WWII, while their brothers are being massacared by the Nazis, the Jews in Palestine joined the British Army. Most Jews served in the "Jewish Brigade". Jews served in other armies, and some were in high positions. The PALMACh made assaults into Lebanon(with agreance from the Brits)
After the war was over, there were many Jews with basic military training. But most Jews were survivers of the worst Jenocide the world had ever known. Many of them saw more killing than a whole army sees in decades. Either way, the Jews were determend not to allow what the Nazis did to happen again. They wanted their own country even more than before the war. The British refused to allow more Jews into Palestine. A campaighn of illigal immigration eagn, with the Haggana serving as a clandestine travel agency. Tens of Thouends were brought in this way. in 1947 the UN decided to part Palestine in to 2 parts, 1 Arab and 1 Jewish/Israeli. The Jews had gotten the smaller part, but were pleased and agreed. The Arabs did not. From 1947 to May of 1948 an internal war was fought between Palestinian Arabs and Palestinian Jews.
The Hagana was used mainly in thedefence, while PALMACH made assaults. In May 1948 Israel announced its independence....
I will continue if you wish, but if its too long and you cant read it ill stop, cause its taking forever.