Parents with violent kids

TodayI have been thinking about violence and kids. Has it always been thus?  Have there always been terrified parents locked in their own bathrooms with a wish and a prayer that they could change it all?
Have you been there, in that bathroom?  Or have you been so very close to it that you knew, just knew, that you had to take action to prevent it happening?
It's a pattern, a long tapestry of increasingly aggressive behaviour from the kids that can lead to that place where they have all the power and you, the parent, have none.
Of course there are degrees of power imbalance in the parent child relationship - what percentage of the power do you have?  60%?  80%? or are you struggling at under 50%? Sometimes the power slips away unnoticed, little by little, until one day you realise that your child is now in control but, because they have so little life experience, the power they have wrested from you overwhelms and confuses them. 
I think back over many years of parent support and how often a 'power issue' arises.  It sounds so simple,  two small words, power and issue. Locked in that bathroom, alone and afraid, it's anything but simple.