Has America Reached Its Peak of Greatness?

I have been thinking on this for a long time, has America reached its peak of greatness? If it has, will it now begin the slow, obvious, and painful decent that leads it to disaster. Just like the great empires before us, Persian, Egyptian, Chinese, Indian, Greek, Roman, and even modern day ones such as France in the Napoleonic era, and the Third Reich and Nazi Germany, are we doomed to their fates of a long string of military defeats resulting in us being carved up as we once were as Colonial America in the middle 1600's and late 1700's, with few victories, a period of gross inflation, and eventually total governmental collapse, paving the way for the next great Nation or Superpower of the world, maybe China v2?

Was Vietnam the first failure? Is Iraq and the War on Terror lined up as the next two? I would certainly like to believe Vietnam was a failure in that we lost our nerve as a nation and felt that one American life let alone 58,000 was a very sad thing indeed. For the other two only time will tell. We are already seeing signs of economic decay and corruption that normally leads to a civilizations downfall, with inflation and the cost of living rates sky rocketing, while the average salary has remained relatively unchanged compared to the other two. The American dollar, once considered one of, if not the most valuable piece of money is now even with the Canadian dollar once 20-30% move valuable then its sister of the North. If the signs continue is the Peso next to surpass us? Will we emigrate to Mexico to escape poverty in the US someday? If the natural order of things holds true here, that what rises to the top must eventually plummet back down, how far will we fall? How long will it take us to reach the point of no-return where nothing can be done to save us? Is the United States of America, doomed to join the other great empires and nations of the past in the pages of History textbooks for children of the world, or will the American spirit hold true and the eagle will continue to soar high across the vast sea of nations and this is just a speed bump on the road to an even higher calling of greatness one where the United States has just begun its ascent?