For several years I was flying on average about once per month. Sometimes that included United Airlines. Always with my luggage I am very careful packing. Even still, more than any other airline, United broke things more often than not. One of the best examples was a brand new hard sided suitcase that was on its second ever segment. One corner was totally crunched and the case was deformed quite badly.
It seems like I’m not alone in my experience that United Airline is a champion at breaking stuff.