Now that the Supreme Court has heard the Proposition 8 and Defense of Marriage Act cases, I made this GIF to show the history of gay marriage in the United States. Red represents a constitutional ban, while blue represents full marriage equality. States in gray either have no same-sex marriage ban or have it banned by statute. This does not include information about civil unions as the main focus is full marriage rights.
The sudden spike in anti-equality states was due to the 2004 Bush re-election campaign using gay marriage as a wedge issue. There was a smaller spike in 2006 to turn up voter turnout for the midterms. Despite the bleak start, marriage equality is starting to go in the right direction. Even if the Supreme Court punts on Proposition 8, four more states; Illinois, Rhode Island, Minnesota, and New Jersey; are ready to bring about marriage equality on their own.
Image base from Wikimedia Commons.