Muhammad was a prophet of the muslims, at age 40 he started having visions. He wanted to conquer and convert as many people as he could.
Arab armies began to swiftly conquer territory in the neighboring Byzantine and Sasanian empires and further.Within about twenty years, they created a massive Arab Muslim empire going across three continents.
All the empires he conquered he converted to the muslim religion.
On June 8, 632 AD, Muhammad died to the disappointment of many people.
Even though muhammad died his armies cept concurring and more and more believed and joined the religion.
Because of all of this, the Muslim religion spread throughout the world to where we are today.