This is why ancient Israel was judged and virtually eradicated from remembrance until 1948. Israel was accountable for receiving God's instructions, knowing them and doing them. A nation that has committed itself to Jesus and His Father from its foundation and then turns its back on Jesus and His Father should expect to receive the same, or worse, for ancient Israel was not gifted with the Revelation of Jesus—and we have been so gifted.
The fact that most American homes have a copy of the Bible carries a responsibility. Americans alone have the full scriptures, free time, and prosperity to study them and practice them--yet do not. Most American Christians don't even know when God is judging their Nation, even though Scripture is clear. For example, we are not to pray against Homosexuality and fight publically to keep homosexuality out of our culture. Doing so is in direct contradiction to God's Judgment on this nation. Don't believe me? Have you even read Romans chapters 1 and 2?
What specifically should believers be repenting for? Along with 1 Peter 4:17, this passage from Romans 1: 29-32 is your answer:
"They have become filled with every kind of wickedness, evil, greed and depravity. They are full of envy, murder, strife, deceit and malice. They are gossips, slanderers, God-haters, insolent, arrogant and boastful; they invent ways of doing evil; they disobey their parents; they have no understanding, no fidelity, no love, no mercy. Although they know God’s righteous decree that those who do such things deserve death, they not only continue to do these very things but also approve of those who practice them."