The LORD speaking to Jeremiah, Chapter 18 says:

"...At one moment I might speak concerning a nation or concerning a kingdom to uproot, to pull down, or to destroy it; if that nation against which I have spoken turns from its evil, I will relent concerning the calamity I planned to bring on it. “Or at another moment I might speak concerning a nation or concerning a kingdom to build up or to plant it; if it does evil in My sight by not obeying My voice, then I will think better of the good with which I had promised to bless it..."

America was founded [planted] by those choosing to worship without interference from the ruling authorities. Sailing to an unknown land, trusting God to lead them in the way He would have them to go, they founded this once great nation.

The years since the "planting" of America have seen drastic changes in this nation. Religious freedom has been replaced by religious tolerance. Commitment to God has been replaced by self-gratification, prosperity messages and seeker sensitive theology. Abortion and homosexuality have become the law of the land. The Bible has been removed from court house, school room and many churches as they teach a gospel not found in scripture. 

America has done evil in God' sight and now in 2013 it would appear that the LORD is thinking better of the good with which He promised to bless.