NEW HAVEN — THE Supreme Court’s soaring decision to strike down the Defense of Marriage Act as unconstitutional is a civil rights landmark, but the history leading up to it is poorly understood. Marriage equality was neither inevitable nor, until recently, even conceivable. And the struggle to secure it was not, as is commonly believed, a natural consequence of the gay liberation movement that gained steam in the late 1960s.

It was not until the 1980s that securing legal recognition for same-sex relationships became an urgent concern of lesbians and gay men. In the 1950s, such recognition was almost unimaginable. Then, most states criminalized gay people’s sexual intimacy. Newspaper headlines blared the State Department’s purge of homosexual employees during the McCarthy-era “lavender scare.” Police cracked down on lesbian and gay bars and other alleged “breeding grounds” of homosexuality.

The lesbian and gay liberation movements of the early 1970s did not make marriage a priority — quite the opposite. Activists fought police raids, job discrimination and families’ rejection of their queer children. Most radical activists scorned the very idea of marriage. But a handful walked into clerks’ offices across the country to request marriage licenses. State officials suddenly realized that their laws failed to limit marriage to a man and a woman; no other arrangement had been imagined. By 1978, 15 states had written this limitation into law....