Late Madinan verse.
9:111 “Indeed, Allah has purchased from the believers their lives and their properties [in exchange] for that they will have Paradise. They fight in the cause of Allah, so they kill and are killed. [It is] a true promise [binding] upon Him in the Torah and the Gospel and the Qur’an. And who is truer to his covenant than Allah?
So rejoice in your transaction which you have contracted. And it is that which is the great attainment.” – Quran 9:111
9:111 – God has indeed promised those believers who strive in his cause and do good in this life that they will be rewarded with Paradise. The part of the verse where it states, “so they kill and are killed”, should be understood in the historically as of those martyrs who actively defended innocent lives from being killed, by fighting tyranny and oppression. The verse should not be understood to mean that it gives open permission killing innocents.
This is prohibited (haram) in Islam. The Prophet (p) never in his life fought against anyone who never waged war against him or his people. For anyone to take this verse to mean otherwise, is going against God and the Prophet’s teachings.
Prophet Muhammed said:
“O God! Let us enjoy our hearing, our sight and our power as long as you keep us alive and make our heirs from our own offspring, and make our revenge RESTRICTED TO THOSE WHO OPPRESS US, and support us AGAINST THOSE WHO ARE HOSTILE TO US let no misfortune afflict our Deen: let not worldly affairs be our principal concern, or the ultimate limit of our knowledge, and let not those rule over us who do not show mercy to us.” – (Riyad as-Salihin Book 5. Hadith 834)
Maulana Muhammad Ali:
“111a. The promise which is said to be binding on Allah, as laid down in the Qur’an, as well as in the previous books, is this, that Allah will grant the believers His blessings, if they exert themselves with their persons and their property in His way: “Allah has bought from the believers their persons and their property — theirs (in return) is the Garden”. The Gospels give the same promise:
“If thou wilt be perfect,” said Jesus to a wealthy man, “go and sell that thou hast, and give to the poor, and thou shalt have treasure in heaven: and come and follow me” (Matt. 19:21). “Behold, we have forsaken all and followed thee; what shall we have therefore?” said Peter. Jesus’ reply was:
“Every one that hath forsaken houses, or brethren, or sisters, or father, or mother, or wife, or children, or lands, for my name’s sake, shall receive a hundredfold, and shall inherit everlasting life” (Matt. 19:27–29).
Moses’ teaching contains similar promises. For instance, the promise of God, “that ye may increase mightily … in the land that floweth with milk and honey,” is made conditional on “thou shalt love the Lord thy God with all thy heart and with all thy soul and with all thy might” (Deut. 6:3–5), which is the same as exerting oneself to one’s utmost in the way of God with one’s person and property.
It should be borne in mind that the words they fight in Allah’s way, so they slay and are slain, are not a part of the promise, but are expressive of the condition of the Companions, and show that they were true to their promise.
The promise to spend one’s person and property may be carried out in various ways under different circumstances, and the Companions of the Holy Prophet were as true to this promise during the thirteen years at Makkah as during the ten years at Madinah.” 
Scholar Abdullah Yusuf Ali:
“1361 In a human bargain both sides give something and receive some advantage. In the divine bargain of Allah with man, Allah takes man’s will and soul and his wealth and goods, and gives him in return everlasting Felicity. Man fights in Allah’s Cause and carries out His will.
All that he has to give up is the ephemeral things of this world, while he gains eternal salvation, the fulfilment of his highest spiritual hopes-a supreme achievement indeed (C/. 61:10-12).
1362 We offer our whole selves and our possessions to Allah, and Allah gives us Salvation.
This is the true doctrine of redemption; and we are taught that this is the doctrine not only of the Qur’an but of the earlier Revelations-the original Law of Moses and the original Gospel of Jesus. Any other view of redemption is rejected by Islam, especially that of corrupted Christianity, which thinks that some other person suffered for our sins and we are redeemed by his blood. It is our self-surrender that counts, not other people’s merits.
Our complete self-surrender may include fighting for the cause, both spiritually and physically. As regards actual fighting with the sword there has been some difference in theological theories at different times, but very little in the practice of those who framed those theories. The Jewish wars were ruthless wars of extermination.
The Old Testament does not mince matters on the subject. In the New Testament St. Paul, in commending the worthy fruits of Faith, mentions Gideon, Barak, and other warriors of the Old Testament as his ideals, “Who through faith subdued kingdoms . . . waxed valiant in fight, turned to fight the armies of the aliens . . .” (Hebrews, 11:32-34).
The monkish morality of the Gospels in their present form has never been followed by any self-respecting Christian or other nation in history. Nor is it common sense to ignore lust of blood in unregenerate man as a form of evil which has to be combatted “within the limits set by Allah” (9:112). (R).” 
 The Holy Quran, Arabic Text with English Translation, Commentary and comprehensive Introduction [Year 2002 Edition] by Maulana Muhammad Ali, Page 425 – 426
 The Meaning of The Noble Qur’an by Abdullah Yusuf Ali, page 124