DOMA overwhelmingly passed both chambers of Congress before heading to Clinton's desk.
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"It was at a time when politicians were using the lives of same-sex couples, lesbian and gay people, bisexuals as a political football," said Camilla Taylor, litigation director at Lambda Legal, which focuses on civil rights for the LGBT community.
The law also mandated states that banned same-sex marriages did not have to recognize same-sex marriages performed in other states.
"What that law told me as a young person coming out to myself and to others was that I was a second-class citizen in this country," said Brian C. Johnson, the CEO of Equality Illinois.
The U.S. Supreme Court struck down DOMA's definition of marriage in 2013. And in 2015 it ruled that the Constitution grants same-sex couples the right to marry.
"I am grateful for the opportunity to be married," said Kat Hindmand, who married her wife 5 years ago on their 20th anniversary of becoming a couple.
Johnson and his husband have a 3-year-old daughter. He said he's thankful how far this country has come on same-sex marriage.
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*"There is hardly a day that goes by that I don't wake up in absolute wonder and gratitude for the life I have," he said.
But some LGBTQ rights activists warn some challenges remain for same-sex couples.
"There's still lots of battles for hearts and minds when it comes to LGBTQ people," said Kim L. Hunt, the executive director of the Pride Action Tank.
Taylor said some are working to turn back progress on marriage equality.
"Recently anti-gay advocates just last week put in a brief before the Supreme Court asking the Supreme Court to revisit its decision in 2015," she said.