Which U.S. Supreme Court case struck down the Defense of Marriage Act?

United States v. Windsor struck down Section 3 of the Defense of Marriage Act.

In 2013, the Supreme Court ruled 5–4 that DOMA’s federal definition of marriage as only between a man and a woman violated the Fifth Amendment’s guarantee of equal liberty. The case arose after Edith Windsor was denied a federal estate-tax exemption following the death of her wife, Thea Spyer, whom they had legally married in Canada.

The decision required the federal government to recognize same-sex marriages that were valid under state law, but it did not itself invalidate every state ban on same-sex marriage. That broader constitutional question was resolved two years later in Obergefell v. Hodges.

Romer v. Evans concerned discrimination against gay and lesbian people in Colorado, while Lawrence v. Texas struck down laws criminalizing private consensual same-sex intimacy. Those cases are related landmarks, but neither directly invalidated DOMA.