Answer: Through War
Explanation: Spread of Islam. After Mohammed's death, the Muslims chose a new ruler, or caliph, meaning successor. The first caliph, and those who succeeded him, spread Islam throughout as much of the world as the Muslim armies could conquer.
In the years after Mohammed's death, the Muslim armies swept north and conquered Syria and Iran. They conquered Egypt and the northern coast of Africa. They succeeded in crossing the Strait of Gibraltar and conquered Spain in the early A.D. 700s. Europe was in great danger of falling under Islamic rule.
In A.D. 732, the Muslims attacked France, but they were stopped at the Battle of Poitiers (also called the Battle of Tours). This was one of the most important battles in history. If the Muslims had won, all of Europe would have been open to their armies. Charles Martel, grandfather of the great Frankish king Charlemagne, led the army that defeated the Muslims.
The Muslims were unable to conquer Europe, but they continued to hold Spain for over 700 years until the Catholic monarchs Ferdinand and Isabella captured the last Muslim stronghold in 1492.
The Muslims continued to spread their empire to the east. Afghanistan and Pakistan were conquered. Eventually, Turkey and the last remains of the Eastern Roman (Byzantine) Empire were conquered as well. The Muslims captured the city of Constantinople in 1453.
As they became more powerful, the caliphs became wealthy and lived in great luxury. They were less interested in religion and more interested in their own pleasure. The empire was divided as Muslims fought among themselves for power. By the 900s, the caliphs were no longer the one ruler of Islam. Great Muslim empires continued for a time in Turkey, Spain, India, Iran, and Egypt. The Islamic world has not been united since.