What event allowed Calvinism to be recognized as a legitimate form of religion alongside Lutheranism and Catholicism?

The event that allowed Calvinism to be recognized as a legitimate form of religion alongside Lutheranism and Catholicism is the Peace of Westphalia. This treaty, concluded in 1648, ended the Thirty Years' War in Europe and also addressed various territorial and religious disputes. It established a principle of co-existence among different Christian denominations, acknowledging the rights of Calvinists as well as Lutherans and Catholics to practice their faith without persecution.

The significance of the Peace of Westphalia lies in its establishment of a new political and religious order in Europe, which included the recognition of Calvinism as a valid faith. This was a pivotal moment in the history of religious tolerance and political sovereignty, effectively allowing for a more pluralistic society in terms of religion within the Holy Roman Empire and beyond.