I realize God is in control of all things -- rulers, authorites, etc. -- and that his eye is constanly roaming the earth looking for souls to strengthen and discipline. Is it fair to say that if we as an American society continue to allow cultural sin, such as abortion, gay marriage etc, he will allow the overthrow and devastation of our "Christian" nation as he did the Jews when they were carted off to Babylon? I hear this mentioned many times on TV and wonder about it as I read the Old Testament.

The answer is no, since the US does not stand in a national covenant with the Lord God.  While it is possible God may punish the US directly, it is more likely he will just leave it to slowly self-destruct. Sin is reflexive, punishing the sinner, right? (See Psalm 7:11; Romans 1:18; Jeremiah 2:19.)