This mistaken assumption is possibly based on the fact that Prophet Muhammad was an Arab, that most of the first generation of Muslims were Arabs, and that the Qur’an is in the Arabic language.
But in actual fact, only about 18 percent of Muslims in the world today are Arabs. The largest Muslim populations are found in Indonesia, the Indian sub-continent and other parts of Asia. Islam is also widespread in many parts of Africa, and there are substantial minorities in Europe, North and South America, and Oceania. Islam is the fastest growing major religion in the world, and its adherents on all continents include both Arabs and non-Arabs.
Further, not all Arabs are Muslims, for there are significant communities of Christian Arabs as well as a number who belong to other religions or profess atheism. While Arab is a geographic and cultural term,
Muslim refers to an adherent to the religion of Islam.
While the revelation was still in its early stages, the Qur’an disclosed that Islam is indeed a global religion. Allah addressed His Prophet therein, saying:
“And We have not sent you but as a mercy to [all] the worlds.” 
“And We have not sent you except comprehensively to mankind, as a bringer of good tidings and a warner, but most of the people do not know.” 
Islam is meant for all people regardless of race, nationality, cultural or religious background. From the commencement of his mission, the Prophet’s companions came from a wide range of lands and races. Among them was an African, a Byzantine, a Persian and a Jewish scholar. All were united in the brotherhood of faith.
There are many references in the Qur’an to the universal nature of Islam. It frequently addresses humanity, saying, O mankind or O people. The Prophet, his companions and their followers made every effort to spread the message of truth to all nations and peoples. He naturally began the propagation of God’s message among his own people, the Arabs, but that does not mean it was restricted to them – rather, only that initially conveying it to those nearest him was the logical first step toward the realization of a long-term goal. Later in his mission when conditions became more favorable, he sent letters of invitation to Islam to the rulers of the Byzantine and Persian Empires, Abyssinia, Egypt, Damascus, Bahrain, Yamamah, Omanand others who represented the influential world figures of the day. Whatever, their response to it, the Prophet’s message was fully acknowledged by the major powers of his time.