Canada became the fourth nation to legalize same-sex marriage on July 20, 2005 (following the Netherlands, Belgium and Spain). By the time the legislation, known as the Civil Marriage Act, was approved, all but two of the country's provinces had already passed legislation in favor of same-sex unions in their jurisdictions (Ontario was the first province to do so on June 10, 2003).
Since then, a dozen more nations have legalized same-sex marriage. In the United States, President Obama announced his support of same-sex marriage in 2012 and one year later the Supreme Court struck down the Defense of Marriage Act (DOMA). Same-sex couples can now marry in eighteen states and the District of Columbia. The combined population of these states is more than 125 million, comprising nearly 40% of the U.S. population.