(CNN) Not too long ago, the question was what states would be among the first to allow same-sex marriages.

But since the U.S. Supreme Court's 2013 ruling invalidating part of the federal Defense of Marriage Act, same-sex marriage rights have surged forward nationwide.

In some cases, such as in Illinois, Hawaii, Minnesota and New York, lawmakers opened the doors voluntarily. In others -- most recently Alabama -- it's been state or federal judges forcing the toehold long sought by gay rights advocates and bitterly contested by those who argue marriage is an institution reserved solely for one man and one woman.

As the dominoes fall in favor of same-sex marriages, the question now seems to be which state will be the last to allow such unions? That's assuming, of course, that the U.S. Supreme Court doesn't get there first by this June, when it is expected to issue its ruling on such bans in four states this spring.

Here's the situation in the 13 states that currently ban same-sex marriages, including eight in which court rulings in favor of allowing same-sex marriage are under review:

Arkansas

The state's constitutional ban on gay marriage, passed in 2004, was struck down twice last year -- once by a state court judge and again by a U.S. District Court judge. Local officials issued some 400 marriage licenses following the state court decision, but the state Supreme Court blocked the issuance of more licenses pending its review of the case. A decision could come soon.

Georgia

Georgia is one of just three states with no legislative action or pending legal decisions whatsoever on same-sex marriage. The others are North Dakota and Nebraska. However, lawsuits are pending to overturn the state's 2004 ban.

Louisiana

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The state's ban is being challenged in state court, where a judge last year ruled the law is unconstitutional, and in federal court, where a U.S. District Court judge took the rare step, for a federal judge, of backing such a ban . The ban remains in place pending Louisiana's appeal of the state court ruling. On the federal level, a ruling is pending out of the U.S Court of Appeals for the Fifth Circuit, which heard arguments in the case in January.

Kentucky

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Last year, a U.S. District Court judge ruled that the state's constitutional amendment banning gay marriages had no "legitimate purpose." The U.S. Court of Appeals for the Sixth Circuit later overturned the ruling , reinstating gay marriage bans in Kentucky and four other states. The Kentucky ban is part of the U.S. Supreme Court case scheduled for arguments in April and a decision by June.

Michigan

Same-sex couples get their marriage licenses at the Oakland County Courthouse on March 22, 2014 in Pontiac, Michigan. A Federal judge overturned Michigan's ban on same-sex marriage on Friday, March 21.

A U.S. District Court judge ruled last year that the state's same-sex marriage ban was unconstitutional, resulting in the issuance of more than 300 marriage licenses. That ended when the U.S. Court of Appeals for the Sixth Circuit granted a stay. The court later reinstated Michigan's ban in the same ruling that reinstated Kentucky's ban. Its fate will be decided by the Supreme Court decision due by June.

Missouri

A state court judge ruled in November that Missouri's 2004 constitutional ban on gay marriage was illegal. Attorney General Chris Koster appealed the ruling to the state Supreme Court. But that court has indicated that it will not rule on the case until after the U.S. Supreme Court decision. Just a few days after that state court ruling, a U.S. District Court judge struck down the state's marriage ban, but that decision has been stayed pending appeals. While the state ban is in effect, officials in the St. Louis area have issued marriage licenses to same-sex couples.

Mississippi

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A U.S. District Court judge granted an injunction last year against the state's same-sex marriage ban, describing it as unconstitutional. The judge, however, postponed his ruling from going into effect to give the state time to appeal. A federal appeals court heard arguments in the case in January. In the meantime, the same-sex marriage ban is still in effect.

Nebraska

A decade ago, a federal court ruled than an amendment banning same-sex marriages was unconstitutional. But the decision was short-lived. An appeals court reinstated the ban. Rights groups have filed legal challenges

North Dakota

Same-sex couples are challenging the state's ban in U.S. District Court, but a federal judge issued a ruling on January 20 delaying the proceedings until after the U.S. Supreme Court rules.

South Dakota

U.S. District Court Judge Karen Schreier struck down the state's same-sex marriage ban in January, but blocked enforcement pending an appeal to the U.S. Court of Appeals for the Eighth Circuit.

Texas

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The state's ban was struck down in January 2014 by a federal judge who said it serves "no legitimate governmental purpose." But, as in many other states, enforcement was delayed pending appeals. The U.S. Court of Appeals for the Fifth Circuit heard the case last month and a ruling is pending.

Ohio

A federal appeals court judge upheld a ban last year on same-sex marriages in the state. That decision is part of the U.S. Supreme Court case expected to be finalized this summer.

Tennessee

In November 2014, the U.S. Court of Appeals for the Sixth Circuit upheld the state's ban. That decision also will be part of the U.S. Supreme Court case.