HONOLULU — When, as most everyone expects, Gov. Neil Abercrombie signs into law same-sex marriage here in the coming days, it may almost seem like a routine event. Hawaii is poised to be among 16 states to approve gay marriage, along with Illinois and shortly after Minnesota, New Jersey and Rhode Island.

But the step in Hawaii has special resonance because the contemporary battle over same-sex marriage was born here two decades ago. Such marriages existed nowhere when Ninia Baehr and Genora Dancel, along with two other couples, filed what seemed like an utterly quixotic lawsuit seeking a marriage license. To near universal shock, Hawaii’s Supreme Court granted them a victory in 1993, ruling that a refusal to allow gay and lesbian couples to marry was discriminatory and illegal.

It was the first judicial expression of an idea that soon caught fire across the country and the world.

The ruling prompted a national backlash, with Congress barring federal recognition of same-sex marriage and dozens of states amending their constitutions to define marriage as between a man and a woman, and it was even overruled by Hawaii’s voters. But it also opened a huge new front for the gay rights movement, laying the groundwork for scores of legal and political battles ever since.