The number of police increased. In our current period, American society has become nothing less than a police state. While women of the past relied upon their husbands for income and protection, the modern women relies on her self and the government for income and protection. Thus, it would appear, that the husband has been substituted with the government. Only there is a twist.
All men now pay for all women and all children.
They do this without receiving the benefit of having the women they support as mates nor the affection of the children. Considering the above, it is clear that single women, generally, vote Democratic because the Democratic Party seeks to replace the husband with the state. Just as strongly we can see why men vote Republican in higher numbers. Men see the state as their enemy. The state appropriates their income, outlaws their natural behavior, and imprisons them if they step out of line.