Common cause of cracked head on a Mazda 2.0 MX 6?

Bought a MX-6 and it was delivered with a cracked head(When we looked at it, it ran and drove fine, sounded flawless)

Anyway, Got the car back to the house after a month, Bought a new head, gasket kit, head bolt set, water pump and timing belt kit. Only reason I got the timing belt and water pump is because we had a civic that had a warped head, because of a bad water pump & eventually the belt snapped. Figured I would go ahead and replace that just too make sure thats not why the head cracked.

I would just like to know, What are some reasons why your MX head cracked. Or what are some things to look out for while changing the head and water pump?

I know its not gonna be too much different than working on a civic, its a 4 cyl. But everything is backwards. Its like going from Chevy 350sb to Pontiac 400bb, Everything is opposite. Its uncharted areas to me.