Why did Iverson leave the NBA?

I'm 20 years old, and in his prime I was too young/didn't understand the game fully yet. What was the reason he left? What was the reason he didn't have any success with the other teams he went to after the Phila 76ers? I was just watching his highlight reels on YouTube & this guy was DOPE. I don't know his story, but if anyone could have been better than Michael Jordan, it was AI. If you say no way, think about this. In Jordans days, double teams were illegal. Allen Iverson embarrased everyone on the court. Thanks guys, I just need his career broken down for me, play-by-play.