In the United States, same-sex marriage has been legal nationwide since June 26, 2015, when the United States Supreme Court ruled in Obergefell v. Hodges that state-level bans on same-sex marriage are unconstitutional. The court ruled that the denial of marriage licenses to same-sex couples and the refusal to recognize those marriages performed in other jurisdictions violates the Due Process and the Equal Protection clauses of the Fourteenth Amendment of the United States Constitution. The ruling overturned a precedent, Baker v. Nelson.
While civil rights campaigning took place from the 1970s, the issue became prominent from around 1993, when the Hawaii Supreme Court ruled that the prohibition was unconstitutional. The ruling led to federal actions and actions by several states, to restrict marriage to male-female couples, in particular the Defense of Marriage Act (DOMA). During the period 2003 - 2015, various lower court decisions, state legislation, and popular referendums had already legalized same-sex marriage to some degree in thirty-eight out of fifty U.S. states, in the U.S. territory Guam, and in the District of Columbia. In 2013 the Supreme Court overturned a key provision of DOMA, declaring part of it unconstitutional and in breach of the Fifth Amendment in United States v. Windsor because it "single[d] out a class of persons" for discrimination, by refusing to treat their marriages equally under federal law when state law had created them equally valid. The ruling led to the federal government's recognition of same-sex marriage, with federal benefits for married couples connected to either the state of residence or the state in which the marriage was solemnized. However the ruling focused on the provision of DOMA responsible for the federal government refusing to acknowledge State sanctioned same-sex marriages, leaving the question of state marriage laws itself to the individual States. The Supreme Court addressed that question two years later in 2015, ruling, in Obergefell, that same-sex married couples were to be constitutionally accorded the same recognition as opposite-sex couples at state/territory levels, as well as at federal level.
By the time that same-sex marriage became legal nationally, public opinion on the subject had reached almost 60% approval levels according to polls by the Wall Street Journal, Human Rights Campaign, and CNN, having been consistently over 50% since 2010 and trending consistently upward over the years prior.