Why did iPhone sync through iTunes delete my entire iCal data?

I just synced my iPhone to my MacBook Pro throuh iTunes and it deleted my ENTIRE iCal data!!! I am in such a PANIC because it deleted all of the data for the last year and did not put it on my iPhone either.

How could this happen...isn't "syncing" supposed to match things up or duplicate...but NOT DELETE everything?!?!?!

Please help...is there any way to restore? I kinda thought that by syncing I would then have a back up on my iPhone as well as the original on my computer.

Any help will be greatly appreciated!!

HOPING!!