Brake Snapped

[bjrscj]

While I was riding to work the other day, I braked to slow down before turning onto a side road. All of a sudden, my rear brake pedal kicked up into my foot. It felt like somebody took a hammer and hit the bottom of my foot. It didn't take long to see what had happened. I'm not clear on all the terminology, but it appeared as though a support arm that was connected to the brake had its bolt snap, dislodging it. The arm on the drum that connects the line to the brake pedal is also bent.

I guess I have two questions on this. First, what is the extent of the damage? I assume I'll need a new drum, since the arm is bent on it. I also assume I'll need a new line from the rear brake pedal to the drum. But my second, more important question, is why did this happen? I don't want to fix this only to have it happen again. I did just replace my rear wheel myself, but after hooking everything back up, it ran perfectly for several hundred miles. I am by no means saying I couldn't have made a mistake, I just thought that would have shown itself earlier. Anyway, I'm looking forward to your advice and insight.