A long time ago, people from different parts of Asia and Europe had lots of contact with each other. Sometimes they were friends, and sometimes they fought. Two big empires, the Sasanian Empire and the Byzantine Empire, often had conflicts and blocked the land routes. So, merchants started traveling by sea instead. Along the sea routes, cities like Mecca and Medina grew and became important.
In Mecca, there was a merchant named Muhammad. He started a new religion called Islam. He said he was a prophet sent by Allah, and there is only one God. Muhammad began teaching people about Islam after he received messages from Allah through an angel. People who believed in Muhammad and followed his teachings became Muslims.
At first, only a few people believed in Muhammad, but over time more and more people joined his religion. Some rich people in Mecca didn't like this because Muhammad said their gods were false. So, Muhammad and his followers left Mecca and went to a city called Medina. This journey is called the 'Hejira' and is very important to Muslims. In Medina, Muhammad became a strong leader and eventually returned to Mecca and made it part of the Islamic Empire. After Muhammad died, the Islamic Empire continued to grow.