You can perhaps judge the rise and decline of a society by the quality of its public intellectuals. In the last century, the United States had some genuinely great thinkers such as Walter Lippmann and Hannah Arendt who addressed a literate public while producing enduring works that can still be read today with great benefit. Now you have people like Francis Fukuyama and Sam Harris who may be studied in the future more as a symptom of their society.