Given how few high schools in the U.S. teach history of the 20th century, I am not surprised by the small number of Americans who understand this. The world in 1946 was ours for the taking, and we took it. But as soon as those other countries began to recover, life got more complicated. First the competition came from Germany, whose automobiles were obviously better than ours. Then came Japan, whose electronics were obviously better than ours. Then came China. It took them longer because the Japanese did horrendous things to China in World War II and then Chairman Mao shredded his country with his Cultural Revolution of the 1960s. But the Chinese are resilient and persistent.
Meanwhile we now see that our purported adversary to the death, the Soviet Union, was an economic weakling all along. Deprivation during World War I caused the Russian Revolution. The Russian people had not recovered when Stalin's Great Purge killed a million or two in 1936-1938. In terms of casualties and destruction, the Soviet Union was the big loser in World War II in every respect. Although Stalin grabbed a lot of territory in 1945-1948 and the Russians did develop the bomb, they were never a serious economic threat. Only the late discovery of natural gas makes Russia relevant to today's world economy.
The late historian Stephen Ambrose made waves in the 1970s when he said in plain language that the U.S. was the big winner of World War II. Americans were not accustomed to hearing the message in those terms, but he was bang on. Prior to 1939, the U.S. was merely one of many players on the world scene; for decades after, we were the unchallenged number one. But now the U.S. represents only 24% of the world's economy. Europe has the same 24%. China has 12% and continues to grow rapidly. You cannot turn the clock back to the 1950s because that decade was a fluke.
And if you smugly say that the U.S. retains technical superiority, are you aware that one-third of the patents filed worldwide last year came from China?
Yes, we still have a measure of military superiority, but at no time since 1945 have we been able to impose our will anywhere without cost. North Korea still exists, our intervention in Vietnam was a total failure, and more recently our interventions in the Middle East have done little to entrench peace and tolerance. Note that to achieve such a measure of military superiority, we spend $10,000 per household in America on our military each year. Other nations are able to spend that money on infrastructure, health care, education, or quality of life.
I am no fan of the messiah of many hardcore conservatives, Ayn Rand, but I believe she would puke in the toilet if told that Americans are taxed at $10,000 per household per annum to sustain a standing military. That's not what she left Russia for.
As for making America great again, I prefer this version over President Trump's (language NSFW):