Why is the majority of Iran Shia?

I don't understand, was Iran Shia due to the overthrowing of Saddam, or was this something that happened way back when due to some other event?

Iran is shia because the Ayatolla was able to take control during the overthrow of the Sha.  They rallied a group of people to overthrow the American Embassy, we got pissed off and set Saddam up to fuck them up.  Saddam fell, Shia came out of the woodworks from whence they were hiding, now this.  Also we forgot Poland.