O.K. I guess that's enough fun. Actually, your question, as innocent as it may seem, would require a semester or more of close study before you can even begin to phatom a guess.
And there have been books, government studies and scholarly papers written on the subject. So, to simply offer an answer would do a disservice to all those victims of domestic violence in the world.
There is however, a very good study of the history not only of Domestic violence in this country, but also of the role of governmental intervention.
David Peterson del Mar, What Trouble I Have Seen: A History of Violence Against Wives, Cambridge: Harvard University Press, 1996. Pp. 244 + ix. $39.95 cloth; 16.95 paper (ISBN 0-674-95076-3; 0-674-95078-X).
Check Amazon for the book or ask your local bookstore to order it. I recommend it as a good read. And for the next time you have a homework assignment that you would like this board to answer