Islam is not just a religion, it is a way of life, and so it differs from other religions in many ways. When you accept that your money, your job, your family, your life, your soul, and indeed your all, belong to God Almighty, you understand that you are indebted to God in a way you can never be to anybody else. This acceptance entails a responsibility on your part to abide by God's commands in every walk of your life.
Islam means to "surrender to God". It also means the peace that one attains by completely surrendering to the All-Merciful God and not to anybody else. By being a Muslim, a person accepts the Noble Quran, which Muslims believe is the word of God, and Prophet Muhammad (peace be upon him) as his or her leader and exemplar. Thus, Islam requires one to declare:
[My prayer, my sacrifice, my life and my death are for God, the Lord of the Worlds.] (Al-An`am 6:162) The foregoing implies that you cannot split up your life into two segments and say, "this is for God, and this is for me". If you do so, what you keep back for yourself will be for Satan, the principle of evil.
That is to say, all spheres of your life are to be devoted to God. No area of your life is exempt from Divine guidance. God has sent His guidance to mankind through His prophets and those who accept that guidance should understand that it covers all aspects of human life. So politics is not exempted from religion.
There is a statement in the Gospels attributed to Jesus (peace be upon him): "Render to Caesar the things that are Caesar's, and to God the things that are God's..." (Mark 12:17, New International Version)
Christian theologians interpret this verse to mean that Jesus did not want any mix-up between religion and politics. But if we study the context in which Jesus said those words, we can clearly see that the interpretation is quite incorrect.
Also, remember that Jesus himself was arrested, according to the Bible, for claiming that he was the Son of God. Can we say that the Romans were mixing politics and religion here? In that case, one wonders what Pilate meant when he said that he did not see why Jesus should be crucified.
The point is: Jesus and all the prophets of God (peace be upon them all) preached that we should have one set of values for all our activities, whether political, economic, or cultural. And those values must necessarily be derived from religious teachings, such as truth, justice, and love.
Will Church interpreters consider it wrong if I say that Jesus wished to free the Children of Israel from the wicked oppressive rule of the polytheists, the Romans? How could the Children of Israel submit to the sovereignty of the Roman emperor and at the same time submit to the sovereignty of Jehovah, as pious Jews are expected to?
Isn't Jesus (peace be upon him) himself a victim of the Roman oppression? Didn't they kill John the Baptist? When such blatantly atrocious crimes against God and His prophets were being openly committed by the invading rulers from outside, and that too in the land promised to the children of Abraham, was there no call to wage a "just war"?
If Jesus meant to say that the Children of Israel should go on suffering under the Romans without a demur, paying their dues and obeying their dictates (which often verged on polytheistic practices), what is the earthly purpose of his religion? Doesn't he want a world of justice and equity?
What is the point of the law of God preached by Moses and all the prophets then? Did Jesus mean to replace the Old Testament with this New Testament of submission to polytheism, to evil, to Satan?
Let us talk about religion and politics: You state that "many nations were converted to Islam by violence and harsh persecution". You must have been listening to the likes of Pat Robertson. I request you to study what Islam preaches and compare it with any other religion in the world and come to your own conclusion.
But you should study Islam not from the enemies of Islam, but from the original sources of Islam: the Noble Quran (you may refer to the translations of Dr. M.A.S. Abdel Haleem or Muhammad Asad), and the sayings of Prophet Muhammad (peace be upon him).
Do you think that a religion propagated by violence and persecution would keep on spreading, even when the force used for its spread is taken away?
The U.S. Center for World Missions estimated in 1997 that the percentage of humans who regard themselves as Christians rose from 33.7% in 1970 to 33.9% in 1996. Its total number of adherents is growing at about 2.3% annually. This is approximately equal to the growth rate of the world's population. Islam is growing about 2.9%.
You may also read the article, "Islam: The Next American Religion?" by Michael Wolfe. (Accessed on October 5, 2011.) The Noble Quran clearly says, [There is no compulsion in religion.] (Al-Baqarah 2:256) So any Muslim who wants to propagate Islam by the use of violence or persecution is acting against the Quran. And such a person, on that score, has gone out of Islam. History itself bears ample testimony for those who used violence for conversion, and why they failed in winning over of the hearts of the people for that reason.
Conversion is a change of heart; it can never be imposed from without. Compulsion can only create hypocrites, not real followers of a religion.