Justice Kennedy covers the history and purpose of DOMA legislation passed by Congress and signed into law by President Clinton in 1996 in United States v. Windsor 570 U.S ___ (2013).
Congress sought to prevent what it perceived as pending recognition of same-sex marriages being considered by a few states, particularly Hawaii, from having any federal recognition. The Windsor case involved $363,053 estate taxes paid by Edith Windsor, which would not have been assessed but for her same-sex marriage recognized by the State of New York, but not recognized by the federal government (IRS) because of DOMA. The Windsor case only decided Section 3 of DOMA.