12. Massachusetts and Same-Sex Marriage (2004)
In 2004, Massachusetts became the first U.S. state to legalize same-sex marriage, directly challenging the federal Defense of Marriage Act (DOMA). This landmark decision sparked a nationwide movement, leading to the eventual Supreme Court ruling that legalized same-sex marriage across the country. For more on how Massachusetts led the way, see the article on the history of same-sex marriage in the U.S (history.com).
