Why did the Jews fight?

Answer 1

Jews have not been engaged in religious conflict since the Bar Kochba Revolts. Jews have been involved in numerous non-religious conflicts in predominantly Jewish Units in both World Wars and in Israel, but these conflicts were based on strategic and political goals. (To have a religious conflict requires one party to wish to impose a religious belief on a different party such as the Thirty Years War or the Islamic Conquest of Iberia.)

Since Jews have not been party to religious conflicts, it is impossible to say what caused them to involve themselves in such things.

Answer 2

Why did the Jews fight whom?

The Jews have had to fight numerous adversaries throughout their 3,000+ year history. Typically Jews fought in self-defense, in the defense of their property, in defense of their countries (when they had them), in defense of non-Jewish countries (when they were permitted to bear arms), and in defense of their faith and practices. For anything with more clarity, an adversary should be specified.