On May 17, 2004, same-sex couples got legally married on U.S. soil for the first time. The day marked a historic step forward for gay people, the freedom to marry movement, and the country. As I describe in my book, Why Marriage Matters, the date made "civil-rights poetry"—the first marriages for same-sex couples came on the 50th anniversary of another civil-rights milestone, Brown v. Board of Education.

Thousands of American same-sex couples have married since that day—but, unlike their non-gay brothers and sisters, most of them have been unable to marry where they live. Because Massachusetts remains the only state, so far, to have ended marriage discrimination, same-sex couples seeking to marry must travel to Canada, Spain, the Netherlands, Belgium, or South Africa. In all of these places, gays have not used up the marriage licenses; there's enough marriage to share, and each marriage in each place demonstrates that families are helped and no one is hurt when exclusion from marriage ends.

In 2004, more non-gay voices spoke in support of the freedom to marry. San Francisco Mayor Gavin Newsom ordered the issuance of marriage licenses there and prompted conversations all across the country as people saw thousands of committed couples line up with their loved ones to get married. Meanwhile, the Bush White House called for a discriminatory federal amendment to the Constitution (happily defeated), and Karl Rove unleashed a wave of state constitutional amendments targeting same-sex couples and their kids.

What you may not know about 2004 is that this epic transformation didn't just come from nowhere.

Same-sex couples have challenged their exclusion from marriage going back to the dawn of the modern gay-rights movement. Within two years of 1969's Stonewall riots, marriage cases were making their way through the courts in three states. But the country wasn't ready, and the denial of marriage was rubberstamped. Once the AIDS epidemic broke the silence about gay lives and revealed gay people as people who love, people who grieve, people who are vulnerable to discrimination because their family ties are unrecognized by law, the climate began to shift. When three couples sued the state of Hawaii for marriage licenses in 1991, it launched a national conversation and movement that continue to this day.

And same-sex couples, of course, were not the first to have to fight against discrimination, and not even the first to fight against discrimination in marriage. As I describe in my book, and on the Freedom to Marry website, marriage has always been a human-rights battleground. This month, in fact, we celebrated the 40th anniversary of the best-named case, Loving v. Virginia, which affirmed marriage as a fundamental freedom and struck down "traditional" race-based restrictions on who could marry whom.

Loving, as well as Brown and Goodridge v. Department of Health, the Massachusetts marriage case, were advances for all of us, gay and non-gay. But then, as now, the struggle between different visions of America—one inclusive and just, the other intolerant and discriminatory—saw every step forward accompanied by attacks and fear-mongering.

In 2004, we saw assaults from a president, a pope, and the unholy alliance of a political party and an anti-gay industry wrapped in false religious garb. Nevertheless, public opinion in support of ending the denial of marriage continues to grow. In 2007, a record number of states considered marriage bills, and a record number enacted measures, such as civil union and partnership, on the road to marriage. One of those states was Washington State, which enacted a "first steps" partnership bill. Now it's time to finish the job in Washington, and in all the other states, with marriage itself.

Evan Wolfson is executive director of Freedom to Marry and the author of Why Marriage Matters: America, Equality, and Gay People's Right to Marry.