You're confusing religion with politics and religious practice with religious belief.
To be a Muslim, all you need is to believe in Allah and Mohammed and all the Holy books and Prophets.
The Sunni Shia schism in the ME is political just as it is in Iraq. It does not exist outside the ME.
Here is a question answered by an Islamic scholar on a Sunni Shia marriage.
Really?
after reading what they do to each other i guess i was wrong-muslims dont kill only those who arent muslims, but each other as well, all they need is a reason. a political reason to behead each other is good as any religious one. what a lovely people muslims are. solving their political differences by killing each other. thanks sam, you really opened my eyes.