When the Supreme Court struck down interracial marriage bans in 1967, only about 20% of the country supported interracial marriage. It wasn't until 30 years later -- in the mid-'90s -- that support climbed over 50%.

So, why did it take so long after the Supreme Court ruled for public opinion on interracial marriage to change -- and yet approval zoomed upward on marriage for LGBTs before the court even got around to ruling?

You can thank three factors, of which the most important is probably visibility. Opinion on marriage for same-sex couples was stagnant all through the '90s, and didn't start climbing until two big things happened: Massachusetts started issuing licenses to same-sex couples, and San Francisco briefly did the same. It was the first time that Americans saw actual couples marrying, and opinion started to change immediately.

The second major change happened after Prop 8 in 2008. Nationally, public support was still under 50%, but there was an intensity of emotion that wasn't there before. After that vote, we saw people become active supporters who had never cared much about marriage before. The groundswell of support allowed several additional states to legalize marriage, and seeing more couples marring spurred further growth in support.

Then came the third factor: a change in the way we talk about why marriage matters. Initially, ads around marriage equality were all about the rights and benefits, but voters heard that and thought that LGBTs married more for legal reasons than for love. When the messages in the ads changed to be about wanting to marry for love and commitment, suddenly, public support started growing even faster.

These days, support is growing so fast that we'll likely see it climb over 60% by the time we elect our next president. That's a stunning rate of growth.

Sometimes, social changes require a little nudge from the law. But when it comes to marriage for same-sex couples, Americans have managed to open their hearts to equality without any help from the Supreme Court.