Loving v. Virginia, decided in June 1967 was the Supreme Court case that mandated an end to anti-miscegenation laws nationwide. Prior to this, different states had different laws.

In the Loving case, Mr. and Mrs. Loving were legally married in Washington, DC yet Virginia didn't recognize the marriage. So, even if there wasn't a DOMA-like law expressly allowing states to ignore marriage licenses from other places, such marriages were at least ignored in Virginia.

Did it happen in a piecemeal manner similar to how gay marriage is currently being fought?

In my opinion, yes it did. I would draw parallels between Pace v. Alabama and Bowers v. Hardwick, both (at the time) standing SCOTUS decisions allowing the banning of interracial relationships or homosexual relationships respectively. Pace was overturned piecemeal by McLaughlin v. Florida, which allowed interracial relationships/cohabitation and Loving, which allowed interracial marriages. Bowers was overturned in 2003 in Lawrence v. Texas, officially allowing homosexual sex in all states. A hypothetical gay marriage legalization case would presumably finish the analogy if it used arguments similar to those in Loving.

Again, that is simply my opinion/interpretation. It remains to be seen how gay marriage cases will progress. This most recent round of cases was largely ducked by the current Court; they deliberately avoided the questions that could have made the decisions about legalization and made narrow rulings. This too, has precedent. McLaughlin and Loving were decided a few years apart by largely the same court, but in '64 the Justices skirted the marriage question for the moment, revisiting it with Loving.