The Muslim community expanded rapidly after the Prophet's death. Within a few decades, the territory under Muslim rule had extended onto three continents--Asia, Africa and Europe. Over the next few centuries this Empire continued to expand and Islam gradually became the chosen faith of the majority of its inhabitants. Among the reasons for the rapid and peaceful spread of Islam was the simplicity of its doctrine. Islam calls for faith in only One God worthy of worship. It also repeatedly instructs man to use his powers of intelligence and observation. Within a few years, great civilizations and universities were flourishing, for according to the Prophet Muhammed (Pbuh) 'seeking knowledge is an obligation for every Muslim man and woman'. The synthesis of Eastern and Western ideas and of new thought with old, brought about great advances in medicine, mathematics, physics, astronomy, geography, architecture, art, literature, and history.
As Muslim civilization developed, it absorbed the heritage of ancient civilizations like Egypt, Persia and Greece, whose learning was preserved in the libraries and with the scholars of its cities. Some Muslim scholars turned their attention to these centers of learning and sought to acquaint themselves with the knowledge taught and cultivated in them. They, therefore, set about with a concerted effort to translate the philosophical and scientific works available to them, not only from the Greek and Syriac languages (the languages of eastern Christian scholars), but also from Pahlavi, the scholarly language of pre-Islamic Persia, and even from Sanskrit, an ancient Indian language.
The achievement of scholars working in the Islamic tradition went far beyond translation and preservation of ancient learning. These scholars built upon and developed the ancient heritage before passing it on to the West.
Muslims excelled in art, architecture, astronomy, geography, history, language, literature, medicine, mathematics, and physics. Many crucial systems such as algebra, the Arabic numerals, and the very concept of the zero (vital to the advancement of mathematics), were formulated by Muslim scholars and shared with medieval Europe. Sophisticated instruments that would make possible the later European voyages of discovery were invented or developed, including the astrolabe, the quadrant and good navigational charts and maps. The Prophet (SAW) said, 'Seek knowledge even into China'.
These facts put us face to face with your question, how Islam spread in the world. However, this is not the most important issue, because there are many ways by which Islam spread, commerce, travel, military confrontation, scholarly interaction, social interactions, and more significantly, the effects of the glorious Islamic civilization on the world. The central question should be why Islam spread quickly and distantly?
The answer to the latter question lies in the nature of the message of Islam itself. The message of Islam is simple, straight forward, and suitable to the innate nature of mankind. It has a clear concept of the oneness of God in contrast to the ambiguity of God’s nature in other religions. The oneness of God in Islam also declared the unity of mankind in their origin, value, and destiny. This revolutionary concept made Islam appeal to many people. Islam also attracted others by its simple five pillars, which make the act of worship easier and clear to the average person. Islam also gave the existence of man a full meaning by declaring the concept of accountability for one’s deeds. Finally, the tolerance of Islam towards non-Muslims, along with the system of ethics in Islam, were virtues that drew people's attention to Islam.
The exemplary life-style of Muslim individuals:
Besides many other reasons which are responsible for the spread of Islam, it is the exemplary life-style and unceasing efforts of individual Muslims to transmit the message of Islam throughout the world which lie at the root of the conquest of the hearts by Islam. Islamic universalism is closely associated with the principle of Amr bi'l-ma'ruf (enjoining the good) for Islam is to be spread by Muslims by means of Amr bi'l-ma'ruf. This principle seeks to convey the message of Islam to all human beings in the world and to establish a model Islamic community on a world-wide basis. The Islamic community is introduced by the Quran as a model community: "Thus, We have made of you an Ummah justly balanced, that you might be witnesses (models) for the peoples, and the Messenger has been a witness for you." (The Quran, 2:143) A Muslim or the Muslim community as a whole thus has a goal to achieve: This is the spread of Islam, conveying the truth to the remotest corners of the world, the eradication of oppression and tyranny and the establishment of justice all over the world. This requires the Muslim to live an examplary life, and thus the moral and ethical values of Islam have usually played an important part in the spread of Islam. Here follow the impressions of the influence of Islamic ethics on black Africans had by a Western writer of the nineteenth century:
How does Islam change the peoples that have accepted it?
As to the effects of Islam when first embraced by a Negro tribe, can there, when viewed as a whole, be any reasonable doubt? Polytheism disappears almost instantaneously; sorcery, with its attendant evils, gradually dies away; human sacrifice becomes a thing of the past. The general moral elevation is most marked; the natives begin for the first time in their history to dress, and that neatly. Squalid filth is replaced by some approach to personal cleanliness; hospitality becomes a religious duty; drunkenness, instead of the rule, becomes a comparatively rare exception...chastity is looked upon as one of the highest, and becomes, in fact, one of the commoner virtues. It is idleness that henceforward degrades, and industry that elevates, instead of the reverse. Offences are henceforward measured by a written code instead of the arbitrary caprice of a chieftain - a step, as everyone will admit, of vast importance in the progress of a tribe. The Mosque gives an idea of architecture at all events higher than any the Negro has yet had. A thirst for literature is created and that for works of science and philosophy as well as for commentaries on the Quran. (Quoted from Waitz by B. Smith, Muhammad and Muhammadanism, pp.42-43)
How did Muslims behave towards the people of the conquered lands?
The Muslim's attitude towards the people of the conquered lands is quite clear in the instructions given by the rightly-guided Caliphs:
Always keep fear of God in your mind; remember that you cannot afford to do anything without His grace. Do not forget that Islam is a mission of peace and love. Keep the Holy Prophet (peace be upon him) before you as a model of bravery and piety. Do not destroy fruit-trees nor fertile fields in your paths. Be just, and spare the feelings of the vanguished. Respect all religious persons who live in hermitages or convents and spare their edifices. Do not kill civilians. Do not outrage the chastity of women and the honour of the conquered. Do not harm old people and children. Do not accept any gifts from the civil population of any place. Do not billet your soldiers or officers in the houses of civilians. Do not forget to perform your daily prayers. Fear God. Remember that death will inevitably come to everyone of you some time or other, even if you are thousands of miles away from a battle field; therefore be always ready to face death.
Many non-Muslims, when they think about Islam, picture religious fanatics on camels with a sword in one hand and a Qur'an in the other. This myth, which was made popular in Europe during the Crusades, is totally baseless. First of all, the Holy Qur'an clearly says "Let there be no compulsion in religion".
In addition to this, Islam teaches that a person's faith must be pure and sincere, so it is certainly not something that can be forced on someone. In debunking the myth that Islam was "spread by the sword", the (non-Muslim) historian De Lacy O' Leary wrote: "History makes it clear, however, that the legend of fanatical Muslims sweeping through the world and forcing Islam at the point of the sword upon conquered races is one of the most fantastically absurd myths that historians have ever accepted." (Islam at the Crossroads, London, 1923, p. 8.). It should also be known that Muslims ruled Spain for roughly 800 years. During this time, and up to when they were finally forced out, the non-Muslims there were alive and flourishing. Additionally, Christian and Jewish minorities have survived in the Muslim lands of the Middle East for centuries. Countries such as Egypt, Morocco, Palestine, Lebanon, Syria and Jordan all have Christian and/or Jewish populations. If Islam taught that all people are supposed to be killed or forced to become Muslims, how did all of these non-Muslims survive for so long in the middle of the Islamic Empire?
Additionally, if one considers the small number of Muslims who initially spread Islam from Spain and Morocco in the West to India and China in the East, one would realize that they were far too few to force people to be members of a religion against their will. Additionally, the great empire and civilization established by the Muslims had great staying power -- its citizens were proud to be part of it. The spread of Islam stands in contrast to the actions of the followers of Christianity, who since the time of the Emperor Constantine have made liberal use of the sword - often basing their conduct on Biblical verses. This was especially true of the colonization of South America and Africa, where native peoples were systematically wiped-out or forced to convert. It is also interesting to note that when the Mongols invaded and conquered large portions of the Islamic Empire, instead of destroying the religion, they adopted it. This is a unique occurrence in history - the conquerors adopting the religion of the conquered! Since they were the victors, they certainly could not have been forced to become Muslims! Ask any of the over 1.8 billion Muslims alive in the world today whether they were forced! The largest Muslim country in the world today is Indonesia --- and there were never any battles fought there! So where was the sword? How could someone be forced to adhere to a spiritually rewarding and demanding religion like Islam?
Mahatma Gandhiji wrote in Young India – 1920:
‘I became more than ever convinced that it was not the sword that won a place in Islam in those days in the scheme of life. It was the rigid simplicity, the utter self-effacement of the Prophet, the scrupulous regard for his pledges, his intense devotion to his friends and followers, his intrepidity, his fearlessness, his absolute trust in God and his own mission. These and not the sword carried everything before them and surmounted every trouble.’
Courtesy - www.thewaytotruth.org & www.islamicweb.com