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?

>>9
Quit whining. You and your religion is all false. I know at this moment you are probably feeling sick as you realise the past 1300 years has all been a lie and countless people and yourself have sufferred for nothing. But I don't give a fuck, you and your race deserve it for being so fucking stupid.