issues that involve parenting and mental issues aren't even 1 percent of the world's problems
Actually, bad parenting can heavily contribute to a large amount of the world's problems. I'll try and name a few.
Teen pregnancy. If parents would bother to listen to their children and try to relate somewhat and understand and not just outright tell their growing teenagers not to do something, then perhaps said teenager would actually listen to the warnings. Or, at the very LEAST, the parent could teach them about safe love early on.
Psychopathic murderers. Chances are, for someone to be THAT messed up, it had to be early on, and there had to be signs, however small. If the parent would watch for these signs and ensure that the child knows that they're loved and cared for, then perhaps there would be less of a sadistic urge later on in life to vent this hatred in the form of blood shed.
Proper morales. Come on.. Really? A large amount of a child's life and morales can be effected by exterior sources, but a parent who actually cares to teach the child proper morales very early on in their life instead of just giving them everything, putting up with their stuff and etc right off the bat can seriously improve their outlook on behavior. This would end a large number of problems that they may have later on, as well as in general take down the number of asshats in the world.
I was exaggerating before with the 90%, but.. Seriously. These are some fairly bad issues that could be fixed with proper parenting.