How has marriage changed since the early 1900s?

Answer 1

In the 1900's it was more frowned upon for a couple to be unmarried or to have a family but without the marital status. That judgment isn't as common in this century, as there are obviously more teenage parents and couples living together but not wanting to get married, and that's pretty normal now :)

Answer 2

Marriage originated as a religious and/or private institution. Governments took it over when the prince figured out he could TAX it. It first started in primitive times just as mating. Then as humans came to religion, the churches stepped in. Finally to be usurped by the state. In both cases it was a way to make money and exert control over people. Prior to that people just lived together because they wanted to. That seems to have worked better for people than the present scheme.