For Toynbee, a civilization might or might not continue to thrive, depending on the challenges it faced and its responses to them.
When a civilization responds to challenges, it grows. Civilizations declined when their leaders stopped responding creatively, and the civilizations then sank owing to nationalism, militarism, and the tyranny of a despotic minority. Toynbee argued that "Civilizations die from suicide, not by murder."
The economic solution of the past 30 years -- the continuous concentration of income and continuous increase of debt -- was never a sustainable solution. The growth of debt and the concentration of income are self-destructive: Neither can last indefinitely. Toynbee would not have accepted these economic policies as a "creative" response.