"If America is not great, what made it great in the first place?"  Most Americans would, indeed, blab the self-serving pap that you, in your next sentence, ascribe to them.  

There were four things that made America great.

The first was a whole continent to expropriate from its Native owners, usually through violence or dishonesty.

The second was sharing borders only with oceans or weak states, so that until we got a military-industrial complex to tell us how we lived every second in mortal danger of Losing Our Freedom, we didn't devote much national capital to the military.

The third was Negro slavery, which earned the export capital that funded Northern industrialization.

The fourth was America's traditional civic peace and long practice in self-government (forget the "freedom" stuff, actual self-governance is where the metal meets the road).

The first three factors are finished; they will not contribute any more to our "greatness."  The fourth is rapidly eroding.