For what reasons did muhammad begin islam?

To call the people to worship only one supreme god, rather than the many idols they worshiped before. He also wanted to bring more equality to the people-- before Islam, women were considered worthless and were even buried alive as newborns. Islam put an end to that. 

Muslims believe that Islam is a faith that has always existed

Since the time there were born it depends, there's fun violence, abuse, r@pe, kidnappings, threats, hostages ect.