In spring, they say, human hearts incline toward love. And from the Midwest to New England, the love that once dared not speak its name is being formally recognized and celebrated.

Just days after the Iowa Supreme Court cleared the way for same-sex marriages in that state, the Vermont state legislature has removed the last barriers to gay and lesbian couples marrying.

While progress in Iowa came via the judicial route, and is likely to spark ongoing political struggles, the victory in Vermont was a political one that comes at the culmination of a long struggle in a state that nine years ago was the first in the nation to authorize civil unions for same-sex couples.

The final stage of that struggle came on Tuesday, after Republican Governor Jim Douglas had vetoed legislation allowing gays and lesbians to marry.

To override the veto, supporters of the legislation needed to muster two-thirds of the vote in the state House and Senate.

They did that with relative ease.

The vote in the House was 100 to 49 in favor of overriding the veto and enacting what was dubbed “An Act to Protect Religious Freedom and Promote Equality in Civil Marriage.”

The vote in the Senate was an even more lopsided 23-5.

Democrats, who control both chambers, Republicans, independents and members of the state’s Progressive Party — members of which have long championed marriage rights — all voted for the override.

The legislative action makes Vermont the fourth state that will permit same-sex marriage. In addition to Iowa, Connecticut and Massachusetts have embraced equality. And, in a related action on Tuesday, the Washington, D.C., City Council voted 12-0 to fully recognize marriages by lesbian and gay couples legally entered into in other jurisdictions. At the same time, the Council voted 12-0 to recognize civil unions and broad domestic partnerships entered into in other jurisdictions as domestic partnerships under the laws of the District of Columbia. (Both the D.C. measures must be approved again on May 5 and, if they are approved by Mayor Adrian Fenty, will face what is likely to be a contentious review by Congress.)

National Gay and Lesbian Task Force executive director Rea Carey hailed the Vermont move as more official recognition — like that of the Iowa Supreme Court — that civil unions are a separate-but-equal compromise that is no longer seen as sufficient or acceptable.

“This is a momentous day and significant turning point in the struggle for the equal treatment of our relationships,” said Carey. “The enactment of this bill affirms that only marriage can provide the protections, dignity and respect that the institution bestows. This vote also recognizes that civil unions simply fall short in ensuring same-sex couples are treated equally under the law.”

Carey also celebrated the fact that legislators, who like Douglas must face the voters next year, backed the override.

That’s evidence of significant political progress in a state where former Governor Howard Dean and a number of legislators found themselves battling a bit of conservative backlash after the civil union law was enacted.

Much of the credit for the progress goes to the Vermont Freedom to Marry campaign, which did terrific organizing work and was on the cutting edge as the bill progressed. Moments after Douglas issued his veto, the Freedom to Marry task force countered with a petition urging an override that had been signed by 17 Vermont CEOs and business presidents, including the heads of Ben & Jerry’s and the Sugarbush ski resort.

Vermont Freedom to Marry board chair Beth Robinson and her colleagues did a remarkable job of highlighting reasons for making the change, countering late-breaking arguments from foes and highlighting allies — particularly Republicans and rural Democrats — who displayed courage as the fight progressed.

Vermont activists proved that it is not just the “activist judges” that social conservatives condemn who are advancing the cause of equality. With sufficient organizing, educating and campaigning, same-sex marriage can win broad political support. Indeed, at the close of the struggle in Vermont, newspapers across the state were editorializing in favor of the legislation and polls showed that 58 percent of Vermonters tended to favor allowing LGBT couples to marry.

The sentiments of the state were summed up by an editorial that appeared in the Brattleboro Reformer newspaper, which took Governor Douglas to task for suggesting that the Legislature did not have time to take up same-sex marriage.

We think that civil rights are not something to be dealt with only when it’s convenient or when the economy is good. No, society must deal with issues like this when it is time to do so.

That time has arrived. There is no longer any reason whatsoever to maintain the second-class status of civil unions.