The founders were pointing to the morality found within the pages of the Bible. Apart from God, your question is unanswerable, or rather, mankind answers it by conquering those that do not follow their morality. Get enough people together that agree with you, and YOU get to determine what is or isn't moral. We have seen this over and over throughout all of human history.
God has told us how this is to be. And don't be confused by looking at the Israel specific commands in the Old Testament- we are in the Church Age and are to be guided by the ministry of the Son of God.