The case looked specifically at bans in Kentucky, Michigan, Ohio and Tennessee and used the equal protection clause of the U.S. Constitution's fourteenth amendment, which forbids states from denying any person "within its jurisdiction the equal protection of the laws."
This has been a long battle.
It was not until 2000 that civil unions were first recognized by any state and not until 2004 that Massachusetts became the first state to legalize same-sex marriage. In 2015, Guam became the first United States territory to allow gay marriage.
As of May, 37 different states have legal same-sex marriage while 13 states banned the practice. This means nearly 72% of the population currently lives in states that allow same-sex marriage. Barack Obama is the first sitting U.S. president to have officially been in favor of same-sex marriage.
Nineteen different countries currently allow same-sex marriage nationwide, with the Netherlands being the first country to legalize it in 2004. In the private sector, Trevor Burgess became the first openly gay CEO of a publicly listed bank in 2014 when C1 Financial (BNK) of Florida, went public on the New York Stock Exchange. In the same year, Apple's (AAPL) Tim Cook became the first openly gay CEO of a Fortune 500 company. Burberry's (BURBY) Christopher Bailey is the only openly gay CEO of a company trading on the FTSE 100.