What was needed to power the 20th century and built the modern world?

Well, the World has changed significantly since the mid 20th century- but yes, there is a definite advantage to not being bombed during a War and the nation certainly benefited from it. 

The USA did not need to rebuild while the European arena was devastated- but dont underestimate the effort that the US put in to rebuilding these countries, even occupying Japan for a period of seven years. BTW, Japan at that time was a manufacturer of cheap toys- and did not have an International car industry. 

The US DID have a plan in place to not only fight against tyranny but to also guide the restructuring after the War (something we neglected to do for Iraq.) Please review the Marshall Plan and the Occupation of Japan for an eye opener... basically, we set up these countries to support themselves and this support system is the basis for modern day globalization. 

The difference is that back in the 1940's/50's- we gave these countries a sense of democracy and self sufficiency -in the example of Japan, releasing them back to their own sovereign power- where in Iraq, we gave people a sense of Imperialism and have yet to find the ability to release the occupation. 

Many persons now feel that the Imperialism in our motives represents the Germany of World War II. We have exhausted our resources and the economy is suffering. Is it possible that another country that remained peaceful could usurp us? Of course. To answer your question, any country that does not conserve its energy within its own borders in time of peace can be usurped by one that is not neglectful of its own systems. 

The economics of this were argued before 1941 and the Japanese attack on Pearl Harbor. Before then, the US was isolationist.