 In Europe, the 1648 Treaty of Westphalia institutionalized the principle of "cuius regio, eius religio"—that rulers of a state had the right to determine the religion of its subjects.This was in an effort to curb the religious warfare that had wracked Europe after the Protestant Reformation.Several of the Thirteen Colonies were confessional states, although of different denominations, before the American Revolution; Connecticut remained one until 1818.