The Koran (or Qur'an), the holy scripture of Islam, is said to have been dictated by God to the prophet Muhammad through the angel Gabriel.  Islam, like Christianity and Judaism, has in its scriptures elements that teach peace and elements that teach war.  The following are excerpts that deal with war.
 

The Holy Qur'an, trans. M.H. Shakir (Tahrike Tarsile Qur'an, Inc., 1983)

SURA 2 - THE COW

[2.190] And fight in the way of Allah with those who fight with you, and do not exceed the limits, surely Allah does not love those who exceed the limits.
[2.191] And kill them wherever you find them, and drive them out from whence they drove you out, and persecution is severer than slaughter, and do not fight with them at the Sacred Mosque until they fight with you in it, but if they do fight you, then slay them; such is the recompense of the unbelievers.
[2.192] But if they desist, then surely Allah is Forgiving, Merciful.
[2.193] And fight with them until there is no persecution, and religion should be only for Allah, but if they desist, then there should be no hostility except against the oppressors.
[2.194] The Sacred month for the sacred month and all sacred things are (under the law of) retaliation; whoever then acts aggressively against you, inflict injury on him according to the injury he has inflicted on you and be careful (of your duty) to Allah and know that Allah is with those who guard (against evil).
[2.195] And spend in the way of Allah and cast not yourselves to perdition with your own hands, and do good (to others); surely Allah loves the doers of good.

[2.216] Fighting is enjoined on you, and it is an object of dislike to you; and it may be that you dislike a thing while it is good for you, and it may be that you love a thing while it is evil for you, and Allah knows, while you do not know.
[2.217] They ask you concerning the sacred month about fighting in it. Say: Fighting in it is a grave matter, and hindering (men) from Allah's way and denying Him, and (hindering men from) the Sacred Mosque and turning its people out of it, are still graver with Allah, and persecution is graver than slaughter; and they will not cease fighting with you until they turn you back from your religion, if they can; and whoever of you turns back from his
religion, then he dies while an unbeliever-- these it is whose works shall go for nothing in this world and the hereafter, and they are the inmates of the fire; therein they shall abide.
 
SURA 4 - WOMEN

[4.74] Therefore let those fight in the way of Allah, who sell this world's life for the hereafter; and whoever fights in the way of Allah, then be he slain or be he victorious, We shall grant him a mighty reward.
[4.75] And what reason have you that you should not fight in the way of Allah and of the weak among the men and the women and the children, (of) those who say: Our Lord! cause us to go forth from this town, whose people are oppressors, and give us from Thee a guardian and give us from Thee a helper.
[4.76] Those who believe fight in the way of Allah, and those who disbelieve fight in the way of the Shaitan. Fight therefore against the friends of the Shaitan; surely the strategy of the Shaitan is weak.
 
SURA 8 - THE SPOILS

[8.12] When your Lord revealed to the angels: I am with you, therefore make firm those who believe. I will cast terror into the hearts of those who disbelieve. Therefore strike off their heads and strike off every fingertip of them.
[8.13] This is because they acted adversely to Allah and His Apostle; and whoever acts adversely to Allah and His Apostle-- then surely Allah is severe in requiting (evil).
[8.14] This-- taste it, and (know) that for the unbelievers is the chastisement of fire.
[8.15] O you who believe! when you meet those who disbelieve marching for war, then turn not your backs to them.
[8.16] And whoever shall turn his back to them on that day-- unless he turn aside for the sake of fighting or withdraws to a company-- then he, indeed, becomes deserving of Allah's wrath, and his abode is hell; and an evil destination shall it be.
[8.17] So you did not slay them, but it was Allah Who slew them, and you did not smite when you smote (the enemy), but it was Allah Who smote, and that He might confer upon the believers a good gift from Himself; surely Allah is Hearing, Knowing.

[8.65] O Prophet! urge the believers to war; if there are twenty patient ones of you they shall overcome two hundred, and if there are a hundred of you they shall overcome a thousand of those who disbelieve, because they are a people who do not understand.
[8.66] For the present Allah has made light your burden, and He knows that there is weakness in you; so if there are a hundred patient ones of you they shall overcome two hundred, and if there are a thousand they shall overcome two thousand by Allah's permission, and Allah is with the patient.
[8.67] It is not fit for a prophet that he should take captives unless he has fought and triumphed in the land; you desire the frail goods of this world, while Allah desires (for you) the hereafter; and Allah is Mighty, Wise.
[8.68] Were it not for an ordinance from Allah that had already gone forth, surely there would have befallen you a great chastisement for what you had taken to.
[8.69] Eat then of the lawful and good (things) which you have acquired in war, and be careful of (your duty to) Allah; surely Allah is Forgiving, Merciful.
 
SURA 9 - IMMUNITY

[9.5] So when the sacred months have passed away, then slay the idolaters wherever you find them, and take them captives and besiege them and lie in wait for them in every ambush, then if they repent and keep up prayer and pay the poor-rate, leave their way free to them; surely Allah is Forgiving, Merciful.
[9.6] And if one of the idolaters seek protection from you, grant him protection till he hears the word of Allah, then make him attain his place of safety; this is because they are a people who do not know.
 
[9.13] What! will you not fight a people who broke their oaths and aimed at the expulsion of the Apostle, and they attacked you first; do you fear them? But Allah is most deserving that you should fear Him, if you are believers.
[9.14] Fight them, Allah will punish them by your hands and bring them to disgrace, and assist you against them and heal the hearts of a believing people.
[9.15] And remove the rage of their hearts; and Allah turns (mercifully) to whom He pleases, and Allah is Knowing, Wise.

[9.29] Fight those who do not believe in Allah, nor in the latter day, nor do they prohibit what Allah and His Apostle have prohibited, nor follow the religion of truth, out of those who have been given the Book, until they pay the tax in acknowledgment of superiority and they are in a state of subjection.
[9.30] And the Jews say: Uzair is the son of Allah; and the Christians say: The Messiah is the son of Allah; these are the words of their mouths; they imitate the saying of those who disbelieved before; may Allah destroy them; how they are turned away!
[9.31] They have taken their doctors of law and their monks for lords besides Allah, and (also) the Messiah son of Marium and they were enjoined that they should serve one God only, there is no god but He; far from His glory be what they set up (with Him).
[9.32] They desire to put out the light of Allah with their mouths, and Allah will not consent save to perfect His light, though the unbelievers are averse.
[9.33] He it is Who sent His Apostle with guidance and the religion of truth, that He might cause it to prevail over all religions, though the polytheists may be averse.

[9.123] O you who believe! fight those of the unbelievers who are near to you and let them find in you hardness; and know that Allah is with those who guard (against evil).
 
SURA 17 -  THE NIGHT JOURNEY

[17.33] And do not kill any one whom Allah has forbidden, except for a just cause, and whoever is slain unjustly, We have indeed given to his heir authority, so let him not exceed the just limits in slaying; surely he is aided.
 
SURA 22 - THE PILGRIMAGE

[22.38] Surely Allah will defend those who believe; surely Allah does not love any one who is unfaithful, ungrateful.
[22.39] Permission (to fight) is given to those upon whom war is made because they are oppressed, and most surely Allah is well able to assist them;
 
SURA 33 - THE CONFEDERATES

[33.60] If the hypocrites and those in whose hearts is a disease and the agitators in the city do not desist, We shall most certainly set you over them, then they shall not be your neighbors in it but for a little while;
[33.61] Cursed: wherever they are found they shall be seized and murdered, a (horrible) murdering.
[33.62] (Such has been) the course of Allah with respect to those who have gone before; and you shall not find any change in the course of Allah.
 
SURA 47 - MUHAMMAD

47.4] So when you meet in battle those who disbelieve, then smite the necks until when you have overcome them, then make (them) prisoners, and afterwards either set them free as a favor or let them ransom (themselves) until the war terminates. That (shall be so); and if Allah had pleased He would certainly have exacted what is due from them, but that He may try some of you by means of others; and (as for) those who are slain in the way of Allah, He will by no means allow their deeds to perish.
[47.5] He will guide them and improve their condition.
[47.6] And cause them to enter the garden which He has made known to them.
[47.7] O you who believe ! if you help (the cause of) Allah, He will help you and make firm your feet.
[47.8] And (as for) those who disbelieve, for them is destruction and He has made their deeds ineffective.
[47.9] That is because they hated what Allah revealed, so He rendered their deeds null.
[47.10] Have they not then journeyed in the land and seen how was the end of those before them: Allah brought down destruction upon them, and the unbelievers shall have the like of it.
[47.11] That is because Allah is the Protector of those who believe, and because the unbelievers shall have no protector for them.
[47.12] Surely Allah will make those who believe and do good enter gardens beneath which rivers flow; and those who disbelieve enjoy themselves and eat as the beasts eat, and the fire is their abode.
[47.13] And how many a town which was far more powerful than the town of yours which has driven you out: We destroyed them so there was no helper for them.

SURA 48 - THE VICTORY

[48.16] Say to those of the dwellers of the desert who were left behind: You shall soon be invited (to fight) against a people possessing mighty prowess; you will fight against them until they submit; then if you obey, Allah will grant you a good reward; and if you turn back as you turned back before, He will punish you with a painful punishment.