States determine marriage laws
(CNN) -- In the United States -- where marriage laws are determined on a state-by-state basis -- the battle over gay marriage began in earnest in 1993, when the Hawaii Supreme Court ruled that the state could not deny same-sex couples the right to marry unless it found "a compelling reason" to do so, and ordered the issue back to the state Legislature.
Courts in Alaska followed Hawaii's lead, and in those two states the court decisions were followed by the adoption of constitutional amendments limiting marriage to heterosexual couples.
The Hawaii ruling prompted several states to pass pre-emptive laws forbidding gays from marrying, often also barring the recognition of a same-sex marriage performed in another state.
Thirty-seven states have enacted some kind of ban on gay marriages, according to Lambda Legal.
The federal government's Defense of Marriage Act (DOMA) -- while not outright banning gay marriage to get around court rulings that bar federal interference in state matters -- affirmed that states are not required to recognize a same-sex marriage performed in another state.
DOMA also effectively bars the federal government from recognizing same-sex unions by defining marriage as "a legal union between one man and one woman as husband and wife" and spouse as "a person of the opposite sex who is a husband or a wife."
Congress passed DOMA in 1996 and two years later voters in Hawaii approved a constitutional amendment banning same-sex marriages.
But the Hawaii court's ruling followed the thinking of a 1967 U.S. Supreme Court ruling that states could not bar anyone from marrying without good reason. That ruling struck down state laws prohibiting interracial marriage, which the court also said violated 14th Amendment guarantees of equal protection.