Is the most effective method in spreading and establishing Islam is war or calling into religion?

In order to evaluate the notion of jihad in Islam accurately, firstly the questions: Who is the Prophet and what is his duty? must be correctly answered. God has sent prophets to guide people on their travel to the Hereafter, which will end either in paradise or in hell. The prominent duties of these messengers of truth are to introduce God to people, to teach them worship, what is halal-permitted and what is haram-forbidden, and to show them how to offer thanks for His boundless favors.

The final Prophet Muhammad (peace be upon him) also fulfilled this duty in the best way, told them about God in Mecca, taught them His commandments and prohibitions, and explained that it is shirk-polytheism (associating partners with God) to worship idols. He showed patience against all kinds of cruelties of unbelievers for exactly thirteen years and finally migrated to Medina with the leave and command of God and continued the same duty there. The idolaters who wanted to hinder his sacred duty did not leave him alone but they could not hinder Islams penetrating into hearts.

An important characteristic of the Final Prophet (PBUH) was his being sahib-us sayf-possessor of sword; i.e. on the way of spiritual enlightening he was also allowed to fight if need be-when his calling into religion was hindered. Among the former prophets, for example, David and Solomon also supported their spiritual jihad with sword.

When history is scrutinized objectively, it is seen that the basic factor in Islams dominating hearts and souls is not war but exhortation; i.e. explaining the truths of Quran to people and showing its beauties. Historians unit upon the fact that two groups of people have great share in Islams spread. The first one is the learned and knowledgeable people who dedicated their lives to explaining Islam and who went to far-off lands when it was needed. The other is merchants who carried the beauties of Islam to the countries they went to with the purpose of commerce.

These verses clearly show that Islam has spread by way of call and offer not with sword:
There is no compulsion in the Religion. The right way stands there clearly distinguished from the false. (Al-Baqarah Surah, 2:256)
And so remind and exhort (them), for you are one (whose duty is) to remind and exhort. You are not one to dictate (faith) to them. (Al-Ghaashiyah Surah, 88:21-22)

The proofs of Islams spreading through calling and exhortation are many. We will here suffice with just a few: When Prophet Muhammad (PBUH) began calling into Islam in Mecca he had no material power. Although all the idolaters were enemy to him, he conquered the hearts and minds of believers only with calling into religion and exhortation. Many people from Hazrath Abu Bakr to Omar became Muslims through this way and announced that Islam is a power impossible to defeat. If the companions wanted, they could kill all the idolaters of Quraysh, first Abu Jahl, just in a single night. But they did not do that. Without resorting to terror and anarchy, they continued to call into Islam bearing with all the hardships and ordeals.

The Muslims who migrated to Medina before Prophet Muhammad (PBUH) also called into Islam and laid the ground for many peoples belief. Thus, the basis of Islam was well established in both Mecca and Medina on deliverance of divine truths.

In the coming years, Islam was established in Medina. The idolaters of Mecca accepted Muslims as a power from then on and signed a treaty with them in Hudaybiya. However, the treaty was signed for ten years, but it lasted only for two years and finally violated by the idolaters in Mecca. However, in these two years the number of people entering Islam was more than that of the ones who entered Islam in twenty years from the onset of Islam.

In the following years, the Mongols ended the caliphate of Abbasid; they burned all Islamic sources. However, in no time they themselves began to be Muslims. It is a historical fact that sword had no role in Mongols entering Islam.

Islams spreading in Indonesia, Malaysia and Africa was through calling into religion, not with sword.

Let us come back to our time after this short scrutiny into history: In the last century Muslims has lost their former power in material terms, but Islam has continued its growth without a pause in spiritual terms. Today, it is scientists who accept Islam in all European countries, first of all Germany and England, and in America; and many of these became Muslims only by studying Islam without receiving a direct call or offer.