The Holy Qur’an, which is the Holy Book of Islam very clearly states: (Let there be no compulsion in religion: Truth stands out clear from Error: whoever rejects evil and believes in God hath grasped the most trustworthy hand-hold, that never breaks. And God heareth and knoweth all things.), Surah 2 Verse 256. This means that in matters of religion, force has no place.
Nevertheless, the Qur’an very emphatically speaks about the importance of establishing justice in every walk of life. The relevant Qur’an verse is: (O ye who believe! stand out firmly for justice, as witnesses to God, even as against yourselves, or your parents, or your kin, and whether it be (against) rich or poor: for God can best protect both. Follow not the lusts (of your hearts), lest ye swerve, and if ye distort (justice) or decline to do justice, verily God is well-acquainted with all that ye do.) Surah 4 Verse 135
There are many other verses also which emphasize particularly social justice. We can understand that if we sincerely strive to establish social justice we have to stand against many who are powerful, which at times may lead to conflicts and fighting. Still, in any case, the use of force is the last option.
To give a specific example: If you are driven out of your house, or if you are being attacked for no fault of yours, Islam teaches that you have every right to resist, to fight back. That is the occasion for fighting; there you have to remember one thing: that you are not to exceed the limits. That is to say you are allowed to fight until your rights are restored, and not a minute more.
Islam is a practical religion; it teaches human beings (not angels) how to live here in this world. You may find other religions preaching not to resist evil; but think of the practical consequences of such an idea! In this world, often we are compelled to fight to establish Peace; that is a paradox. But that is the truth.
The aim of our fighting should be the establishment of a just and peaceful society. As long as that is so, fighting is permitted. Otherwise evil will rule!Islam means peace and truly stands for a peaceful and prosperous society where love, mercy, justice and all other values prevail.