When was the institution of marriage invented?

The concept of marriage predates Christianity and the other two forms of Abrahamic religions, Judaism and Islam which share a common origin and common values. Marriage is very ancient dating back beyond recorded history and was practiced by all people of many cultures, ethnicities, and belief systems.

The prevalence of the concept of marriage came to the forefront of culture when humankind evolved from hunter gatherer to agriculture and pastoralism which occurred during the Neolithic/agricultural revolution about 10,000 years ago.

Originally "marriage" was a private, binding contract between clans (families) to form an alliance, thereby increasing the clan's chances for survival in war against rival clans. A "dowry" was given by each clan to "seal the deal". Marriage was contractual, considered a passing of "property" between clans as a symbol of intention to honor the agreement being made. Property took many forms: cattle, land, children, whatever was considered to be of great value at the time. In the United Kingdom, a requirement for a public announcement in a Christian parish (banns of marriage) was introduced by the Roman Catholic Church in 1215. This set the precedent for marriage as is recognized by the Christian community.

The origins of marriage is NOT religious, nor does it have anything to do with the God of the Abrahamic religions. It was around way before organized religion which by Christian standards means it is PAGAN. Christians "borrowed" many pagan rites and rituals so Pagans would convert more readily and easily to Christianity.

In modern times in the United States, before a legal marriage ceremony can be performed, one must obtain a marriage license from government authorities. When a legally married couple seeks a divorce they must go before a judge to have the marriage annulled. Ministers and priests do not issue legally binding marriage licenses, nor do they have the legal authority to grant a divorce. The religious concept of marriage has nothing to do with the legal concept. Church and State are completely separate in the case of the institution of marriage.