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In Massachusetts, the traditional values group Mass Resistance has found that its materials — including a video on what same-sex marriage “did to Massachusetts” — have been of interest to people in Australia, the United Kingdom, France and, recently, Jamaica, said Brian Camenker, president of the group.

In America, gay-rights groups were able to conduct a “blitzkrieg” in some states, thanks to deep-pocketed benefactors and political allies, he said.

Overseas gay-rights advocates “just don’t have that enormous advantage,” Mr. Camenker said. “So that sort of holds them back.”

Although the push started in earnest in 1990 in Hawaii, the Netherlands became the first country to legalize gay marriage in 2000.

Eighteen countries permit same-sex nuptials either nationwide or in certain jurisdictions, says a report by the Pew Research Center’s Religion and Public Life Project. These include several European countries, as well as Canada, South Africa and Argentina.

In England and Wales, gay marriages will begin in March. In the rest of the United Kingdom, Scotland is debating a gay-marriage measure and Northern Ireland has voted one down, the Pew report says.

In Brazil, same-sex marriages have commenced under a ruling from the National Council of Justice, but there is “uncertainty” there because of resistance from legal or political directions, it added.

In the U.S., 17 states — now including New Mexico — and the District of Columbia permit same-sex marriage, thanks to this banner year in which eight states joined the gay-marriage column.

A global gay-rights network called the International Lesbian Gay Bisexual Trans and Intersex Association has been active for decades, and the D.C.-based Human Rights Campaign has said it would be increasing its international efforts.

“Expanding HRC’s ability to work in coalition with international LGBT human rights defenders will hasten the day when LGBT people are free from hate-based violence and equality is a reality for all,” the group’s president, Chad Griffin, said in November as part of an announcement that the Paul E. Singer Foundation and Daniel S. Loeb Family Foundation had given major gifts to fight discrimination in foreign countries.

Mr. Wolfson, referring to the days in the 1990s when he and lawyer Dan Foley assisted three gay couples in their battle for marriage licenses in Hawaii, said it has been a long journey.

Still, he said, “it is very exciting and gratifying to see that what we began in Hawaii has launched an ongoing, global movement.”