Did not Allah check one set of people by means of another, there would surely have been pulled down monasteries, churches, synagogues, and mosques, in which the name of Allah is commemorated in abundant measure. Allah will certainly aid those who aid His (cause); for verily Allah is Full of strength, Exalted in Might, (able to enforce his Will). They are those who, if we establish them in the land, established regular prayer and give Zakat, enjoy the right and forbid wrong; with Allah rests the end (and decision) of (all) affairs.” (Surah Al-Haj ‘The Pilgrimage’ Verses 39 to 41)
In this way, fighting started in Islam, or for this purpose Islam enacted provisions for fighting. The first fighting Muslims engaged in against Quraish was "the battle of Badr" which is mentioned in Islamic history and which took place two years after the Muslims had emigrated from Mecca to Medina. The battle took place at the entrance of Medina to which the Muslims resorted to escaping from the Quraishi armies, which hunted them for no reason except that they opposed their doctrine, abandoned the worship of idols and embraced Islam.