Some Quranic Verses on Jihad

When has permission been given to go to war?

Permission (to fight) is given to those who are being attacked, because they have been wronged. And surely God measures out help for them. - Surah al-Hajj verse 39

And what is with you that you do not fight in the path of God and (in the path) of the oppressed of men and women and children, those who say "Our Sustainer, take us out from this city, its people are wrongdoers, and decree for us a protector, and decree for us a helper". - Surah an-Nisa verse 75

God does not forbid that you do good and make justice for those who do not fight you in the religion or drive you out from your homes. Indeed, God loves those who do justice. God only forbids your friendship with those who fight you in the religion and drive you out from your homes and back those who drive you out. And who befriends them, such are wrongdoers. - Surah al-Mumtahana verses 8-9

When must Muslims seek peace?

Fight in the path of God those who fight you, but do not aggress. Surely God does not love the aggressors. And fight them where you come upon them, and send them out from where they have sent you out, for persecution is a worse thing than fighting. And do not fight them at the Sacred Mosque (in Mecca) unless they fight you there, but if they fight you, then fight them back. That is the reward of the rejectors. Then if they cease, so God is All-Forgiving, Gentle. And fight them until there is no more persecution and the religion is for God. But if they cease, so let there be no hostility except against wrongdoers. - Surah al-Baqarat verses 190-193

And if they incline to peace, so you must incline to it. And trust in God, for He hears and knows all. - Surah al-Anfal verse 61

Surely those who have faith and who emigrated and strove with their wealth and their souls in the path of God, and those who sheltered them and helped, such, they are protecting friends of one another. And those who have faith but they did not emigrate, you do not have any duty of protection over them until they emigrate. But if they seek your help in the religion, then it is on you to help them except against a people with whom you have a treaty. And God sees all that you work. - Surah al-Anfal verse 72

Do not fight those who join a folk with whom you have a treaty, or they come to you with their breasts constricted against fighting you or fighting their own folk. And if only God had willed, He could have given them an authority over you so they would have fought you. So if they stand aloof and do not fight you, and they speak a word of peace, then God has not given you a way against them. - Surah an-Nisa verse 90

O you, those who have faith, when you go out to fight in the path of God, make things clear and do not say to someone who gives you peace, "You are not a believer," - you coveting the pleasures of the life of the world, and with God is abundant reward. You were the same as that before, then God was gracious to you. So make it clear. Surely God is aware of what you do. - Surah an-Nisa verse 94

Also see My Condemnation of the September 11 Terrorist Attacks, What Islam Really Says about Killing the Innocent, and Muslims Condemn Terrorism.