WASHINGTON » The Supreme Court made history today with two victories for marriage equality, in California and nationwide.

In a pair of highly anticipated decisions, the divided court effectively undercut California’s Proposition 8 and struck down the federal Defense of Marriage Act. Though one of the decisions was written narrowly, together they provide an emphatic, if incomplete, win for advocates of same-sex marriage.

The decisions, issued on the final day of the term that started last October, address different issues. In each, a slim 5-4 majority rallied for the position that effectively supported same-sex marriage.

The Proposition 8 case involved a challenge to the California ballot measure that banned same-sex marriage. The court today concluded that the supporters lacked the legal standing to defend the measure.

Standing is the legal term for being eligible to file a lawsuit. To have standing, an individual must have a significant interest in the controversy and must either have suffered an injury or face an imminent threat of injury.

“Because we find that petitioners do not have standing, we have no authority to decide this case on the merits, and neither did the 9th Circuit,” Chief Justice John Roberts Jr. wrote.

The decision leaves intact a trial judge’s order blocking Proposition 8 from taking effect. At the very least, this means that two same-sex couples who filed the lawsuit against the ballot measure may marry. Advocates say that other same-sex couples in California should be able to take advantage of the ruling, though that might require further trial-level clarification.

The court’s majority, though, stopped short of declaring a constitutionally protected right to same-sex marriage nationwide. The justices also declined to take up the Obama administration’s proposal, which would have extended the ruling to a handful of other states that have shared California’s policy mix of allowing civil unions while banning same-sex marriage.

The separate Defense of Marriage Act case involved a challenge to the 1996 federal law that prohibited same-sex couples who had been married under state laws from obtaining a host of federal benefits. A different majority concluded that portions of the law violated the Constitution.

“DOMA divests married same-sex couples of the duties and responsibilities that are an essential part of married life,” Justice Anthony Kennedy wrote. He joined the court’s four liberal justices in the decision.

Section 3 of the Defense of Marriage Act declares that, for the purposes of providing federal benefits, marriage is “only a legal union between one man and one woman as husband and wife” and a spouse is only a “person of the opposite sex who is a husband or a wife.”

The definition is important because it determines eligibility for a host of federal rights, benefits and privileges.

“It affects every aspect of life,” Justice Ruth Bader Ginsburg said during oral argument.

The Government Accountability Office has identified more than 1,100 areas of federal law in which marriage matters, ranging from tax and welfare benefits to employment and immigration. Same-sex military couples, for instance, are denied housing, health insurance and disability benefits, and are ineligible for burial alongside their spouses in national cemeteries.

“The statute is invalid, for no legitimate purpose overcomes the purpose and effect to disparage and injure those whom the state, through its marriage laws, sought to protect in personhood and dignity,” Kennedy wrote.

Twelve states and the District of Columbia now recognize same-sex marriage, and a recent Pew Research Center survey found that 72 percent of those asked thought that legal recognition of gay marriage was inevitable.

While the decisions were read inside the court starting at 10 a.m. EDT, sparking a frantic rush by reporters to figure out what the justices had concluded, a large crowd outside anxiously checked iPhones and Androids for the latest updates.

Each case involved a separate set of facts and distinct legal reasoning.

Proposition 8

The challenge was brought on behalf of several same-sex couples, including Kristin M. Perry and her partner, Sandra Stier, and Paul Katami and his partner, Jeffrey Zarrillo. Both couples were denied marriage licenses in California because of the Proposition 8 ban.

The California case arose after the state Supreme Court ruled that same-sex couples had the right to marry. Voters subsequently changed the state’s constitution in 2008, in the Proposition 8 ballot measure, to limit marriages to those between one man and one woman.

The Obama administration proposed that the court protect same-sex marriage specifically in the handful of states that ban it but accept gay civil unions. The justices, though, showed little interest in this proposal.

After a high-profile, 12-day trial in San Francisco, U.S. District Judge Vaughn Walker issued an unusually detailed, 136-page opinion in August 2010 in which he concluded that Proposition 8 violated the U.S. Constitution.

Walker retired in 2011, at which time he told reporters he was gay and in a long-standing relationship with another man. Conservative supporters of Proposition 8 failed in their subsequent attempt to claim that Walker was biased because of his sexuality.

The 9th U.S. Circuit Court of Appeals upheld Walker’s decision, though for a very state-specific reason that essentially confined its reach to California: The California Supreme Court had recognized same-sex marriage rights in May 2008, and then voters removed those rights in November 2008 by approving the ballot measure.

California state officials declined to defend the same-sex marriage ban. Instead, a conservative former Southern California state legislator named Dennis Hollingsworth and allies argued on the proposition’s behalf.

The California Supreme Court concluded, and the 9th Circuit Court of Appeals accepted the view, that the opponents were authorized to step in since the state had stepped out.

Defense of Marriage Act

The federal law defining marriage inserted the national government into what traditionally had been state territory.

Supporters of the Defense of Marriage Act when it passed included Democratic Sen. Harry Reid of Nevada, who’s now the Senate majority leader, and then-Sen. Joe Biden of Delaware, now the vice president.

The House of Representatives, which passed the bill by an overwhelming 342-67, explained in a committee report that the law was meant to convey “moral disapproval of homosexuality.” One of the law’s chief backers at the time, current Sen. Tom Coburn, R-Okla., said during the House debate that homosexual conduct was “based on perversion and … lust.”

In the years that followed, though, a number of supporters began back-pedaling. The act now is opposed by former Rep. Bob Barr of Georgia, a Republican author of the bill who in July 1996 decried “the flames of hedonism, the flames of narcissism, the flames of self-centered morality (that) are licking at the very foundations of our society: the family unit.”

The Obama administration initially defended the federal law, as is customary for administrations, but it stopped in February 2011 after concluding that Section 3 violated the Constitution. In its place, House Republicans funded the defense of the statute through what’s called the Bipartisan Legal Advisory Group.