Let's deconstruct what you allege Mr. Donovan said, as well as your claim about Michael Donovan. There has never been a Director of Central Intelligence named Michael Donovan (nor has there ever been a Director of Central Intelligence named Doonavan). All the Directors and Deputy Directors of Central Intelligence
are listed on this page. William J. Donovan, known as "Wild Bill" Donovan, was the Director of Strategic Services from 1942 to 1945. The Office of Strategic Services was the "parent" organization from which Central Intelligence was organized in 1945. William Donovan had a law degree from Columbia University, having previously gotten Bachelor of Arts in History from that University in 1905. However, you stated you were quoting "Michael Doonavan," not William Donovan.
The claim that the Roman Empire "fell" in 476 is false. (There is no such word in the English language as "emarier.") The Roman Empire continued to exist, under its own laws and policies, with its own bureaucracy, military and state religion, until the Osmanli Turk Sultan Mehmet captured the city in May, 1453. So if your fictional Michael Donovan had said the Roman Empire fell in 476, he was talking out of his ass. The assumption that industry in the United States would not be possible without petroluem products is false. Where as it is true that many electric generation plants rely upon petroleum, electricity is generated in many, many places in the United States with nuclear power plants, and the possibility of the United States converting entirely to nuclear power in the event of the failure of petroluem reserves is reasonable and very likely--far in the future, when petroleum reserves actually do fail. The assumption that the failure of petroleum reserves would affect the United States, but not China, Japan or Russia is, to say the least, laughable. Japan is far more reliant upon petroleum imports for electric power generation than is the United States. China relies primarily upon large coal reserves. The Russian Federation relies upon petroluem and nuclear power. Were petroleum to fail, none of these nations, other than Japan, would be at risk of economic collapse as a result. The odds are good that Japan would have already switched to nuclear power generation, although Japan has the problem that it does not produce uranium--the United States, however, produces uranium, and would not be threated by the failure of petroleum.
China already is a superpower. Japan will never again be a superpower, unless one alleges that it now is on an economic basis. The claim that Russia would take control of eastern Europe is absurd--they can't even pay their soldiers and sailors now, let alone provide the material resources for the conquest of any portion of Europe. Russia already controls northern Asia, and has done so for more than four centuries.
Even were any part of this silly scenario true, it would not show any corollary with the history of the Roman Empire. This laughable scenario relies upon a contention that the United States will collapse because of a lack of petroleum resources. Apart from that being unlikely, there is no correlative failure of resources which can reasonably be alleged to have caused the final collapse of the Roman Empire. The Roman Empire fell, in 1453, after the rise of the Osmanli Turks, and their seizure of control of Anatolia and the southern Balkan penninsula over a period of more than two centuries. Do you allege that someone will slowly conquer Mexico and Canada, and then take over the United States?
You don't know what the hell you're talking about.