Marriage (or short term variants of it), are a natural thing among humans and other animals. People commit to each other formally or informally in almost all societies.

Equally, in almost all societies people want to control other people's reproduction and sexual behavior, and hence in most societies marriage became controlled by people other than the immediate participants. In most primitive cultures, for example, marriage had to be conducted by the local tribal elder, chief, or religious leader.

In Christian societies, for instance, terms of marriage were dictated by the Christian church.

Many Christian societies went through a separation of church and state, and in the resultant grab for power, the institution of marriage was nationalized by the government. People could still get married in a church, but the government, and not the church, dictated the terms of marriage.

Of course there was no need for government to dictate the terms of marriage any more than there was a need for the church to do it. It was just about controlling the population, by dictating the terms of what was essentially a private contract between two people.

In the second part of the 20^th century, populations in Western countries refused to let the government dictate the terms of their sexuality. People chose to have sex whether they were married or not. The government's reaction, instead of abandoning the idea of interfering in people's lives, simply changed tack. They not only took away the right of individuals to choose their own marriage contracts, by dictating the terms of contract, but (even worse) deemed the contract to have taken place even situations in where it hadn't.

Under Australian law, a magistrate can deem that a de-facto marriage has taken place if someone leaves a toothbrush at a former sex-partner's house.

This kind of interference was gleefully embraced by feminist groups in particular because it gave them the power to control other people's lives, and frequently the assets and incomes of previous sexual partners.

The Australian Family Law Court, under the auspices of helping children, is the mechanism by which this control takes place.