Was the United States founded on Christian Principals?
Well let's look at some of the founding principals of the country:
Democracy?
The ideas of Democracy first began in pagan Greece in 5th century BC and later began to take hold in western europe in the late 1700's after religion's power in government had lessoned.
Secular government?
People can argue endlessly over the entanglements of religion and government but for the most part our government was set up as a secular government and has remained mostly separate from religious affairs.
Freedom of religion?
It is in no religion's interest to make it easy for people to join or explore other faiths.
Unequal rights?
Even thought the Declaration of Independence speaks of all men as being created equal, it was not taken literally. Blacks and Native Americans were not equal with whites, women were not equal with men and men who were not land owners were not equal with those who were.
Many of these ideas of inequality (slavery, subservient women) can be supported by the bible but most modern Christians would not consider these as 'Christian Principals'. [Romans 7:2, Timothy 2:11, 1 Corinthians 14:34]
Slavery?
Like stated above, slavery is supported by the bible but most would not consider that a good Christian Principal. [Leviticus 25:44, Titus 2:9, Ephesians 6:5]

