The historical event that led to the separation of church and state in the United States is the First Amendment of the Constitution, ratified in 1791. This amendment prohibits Congress from establishing a religion (the Establishment Clause) and ensures citizens can freely exercise their religion (the Free Exercise Clause). The principle of separation emerged from Enlightenment ideas and a desire to avoid the religious conflicts that plagued Europe. It aimed to create a pluralistic society where multiple beliefs could coexist without government interference, shaping the American identity and influencing contemporary debates over religion's role in public life.