Has marriage always had the same definition?
Actually the institution has been in the process of constant evolution.
In the stone-age it was to ensure a stable structure for child rearing and controlling sexual conduct, later it was deemed as a means of preserving power such as with kings and other ruling classes, or marrying of daughters to forge alliances, acquire land and to produce legitimate heirs.
People started marrying as long ago as 4000 years ago. Initially marriage was seen as a civil affair governed by Imperial law but then the church took over and elevated marriage to a holy union.
Did love play a role?
For most of the history, love wasn’t seen as part of marriage at all. In fact, love and marriage were once widely regarded as incompatible with one another.
When did romance enter the picture?
In the 17th and 18th centuries, when Enlightenment thinkers pioneered the idea that life was about the pursuit of happiness. They advocated marrying for love rather than wealth or status. People took more control of their love lives, they began to demand the right to end unhappy unions. Divorce became much more commonplace.
Did marriage change in the 20th century?
Dramatically. For thousands of years, law and custom enforced the subordination of wives to husbands. But as the women's-rights movement gained strength in the late 19th and 20th centuries, wives slowly began to insist on being regarded as their husbands' equals, rather than their property. If they were unhappy with each other, they could divorce — and nearly half of all couples did.
Marriage had become primarily a personal contract between two equals seeking love, stability, and happiness.
Now everyone fits under the Western philosophy of marriage.