According to Merriam-Webster dictionary, marriage is "the state of being united to a person of the opposite sex as husband or wife in a consensual and contractual relationship recognized by law." Another definition is a similar state of being united to a person of the same sex.
Historically, in the United States, marriage has been primarily regulated by individual states. However, the overwhelming consensus throughout the country viewed marriage as a mutual agreement between a free man and a free woman to join together as the foundation of a family unit. These individuals could take only one partner as husband or wife at any given time. This understanding was grounded in English common law from which many American legal doctrines originated.
President Bill Clinton signed into law the Defense Against Marriage Act in 1996, which specifically defined marriage as "only a legal union between one man and one woman as husband and wife." The act goes on to declare that the word spouse refers "only to a person of the opposite sex."
These strict definitions of marriage held in America until Friday, June 26, 2015, when the Supreme Court of the United States declared that same-sex marriage was legal in all 50 states.