Most everyone agrees that after thirteen years of preaching his new religion, Muhammad did not have very much success and was forced to flee Mecca with his 150 followers. There he formed an army and returned eight years later to conquer the city that rejected him.
Muslims who are not as knowledgeable about the true record left by the historians of the day believe that Mecca was a city of extreme religious persecution and evil pagans who simply had to be conquered because of the danger they posed. Muhammad then fully forgave the people and everyone lived in harmony, enjoying the new age of peace and religious tolerance that Islam brought to the city.
Today's Muslims have a visceral need to believe that their religion made Mecca a better city, because if Islam wasn't better than the paganism that came before, then it has little chance of being better than Western religion and other alternatives that exist today.
Unfortunately, the picture painted by the early Muslim historians is in stark contrast to what today's Muslims desperately want to believe. The truth is that Islam transformed a highly tolerant and religiously pluralistic city into one of only two in the entire world where one is not even allowed to set foot if they do not profess the predominant religion. (Not surprisingly, Medina is the other).