Why did the Jews and Muslims fight for islam?

Answer 1

Jews never fought for Islam. Jews fought with Muslims on occasion, but far more often had an auxiliary role or fought with Muslims in a Nationalistic context (for a modern Secular Nation-State as opposed to a Theocratic Islamic State).

Several Jewish Tribes fought alongside the Muslims in Mecca-Medina Wars of the 620s C.E. in defense of Medina. Several other Jewish tribes famously fought against the Muslims, even if they were Medinan. They saw such wars and alliances based on local politics and a determination to survive the outcome of the war.

Jews were often pro-Islamic in the early Caliphate period as Muslim governance tended to be less oppressive than the Christian alternative. In many cases, but especially in Spain, Muslim soldiers would not trust the formerly Christian city to remain docile after the Muslim troops departed. This would normally mean that the conquerors would have to leave a rearguard in the city to prevent an uprising. However, since the Jews were in favor of Islamic leadership, Muslims would entrust the endemic Jewish communities of a given city with weapons and the protection of the recently conquered city. In this way, more Muslim troops were free to advance.

This positive Muslim-Jewish Alliance existed from the mid-600s C.E. to around 800 C.E. when the Muslim expansion ended. Jews and Muslims remained on good terms, however, up until the 1800s except for a few minor hiccups (relatively speaking).

Answer 2

Hinduism and Islam have many conflicting practices and beliefs. These practices cause social and political unrest leading to violence and fights.