could talk a lot about Spengler, but details help and i will seed them here.
from Wikipedia on Xenophon, contemporary of Aristotle.
The strength of Cyrus in holding the empire together is praiseworthy according to Xenophon. However, the empire began to decline upon the death of Cyrus. By this example Xenophon sought to show that empires lacked stability and could only be maintained by a person of remarkable prowess, such as Cyrus
Suggests that maybe Clinton and Obama were this type, the bush pair and Trump not capable enough. the danger is that such a capable leader would usually be strong, that is, tyrannical. Chalmers Johnson discusses this in his trilogy on the American Empire.
Dismantling the Empire: America’s Last Best Hope (American Empire Project)