i was driving my 2003 trailblazier and the back passenger side rim spilt in half all the way around . it shattered the roto and caliper was laying in the new ruined tire. wondering what could of caused this . trailblazier has 382,500 miles on it . 2 weeks ago I took off a tire in the rear drivers side that was warbled . it felt like it was driving on a square wheel

 

Are you the original owner? With that many miles on it, you don't know how it was treated or abused unless you are the original owner. Sounds like the other rims are in bad shape also. If you plan on keeping it, you should probably change all 4 rims.