That was a remarkable era for sure. Without America and the courage of Ronald Reagan, the Iron Curtain never would have come down at least for a long time. But there have been many such eras for this county.
Without America, probably WWI and certainly WWII would not have been won by freedom loving people, most of the remainder of the Jews in Europe and the near East would have been murdered, and all of Europe and much of the near East and Africa would be speaking German--most of the Pacific nations would be speaking Japanese. The entire world would be at the mercy of totalitarian nations. The years following the war put the United States on the map as the most forward thinking, innovative, creative, and prosperous nation on Earth. Made in America was the coveted label everywhere. We built great things, invented things, manufactured things, and anybody willing to put in the effort and elbow grease could achieve whatever he/she had the aptitude and determination and courage to do.
But in the 1960's we experienced a counter revolution in which our young people, for the first time in history, totally rejected the culture and values of their parents. They dropped out, tuned out, zoned out and listened to liberal/progressive revolutionaries who put visions of utopia in their heads if they adopted Marxist concepts of a better world. Most rejected much of that as they got older, but it had changed them. It affected them by making them believe that the old values were selfish values and those who got ahead didn't deserve that and somehow cheated everybody else. And instead of looking to government to keep the peace and protect their rights, they began looking to government to provide all that is righteous and good and fair for all. Togetherness replaced individuality and personal responsibility. And liberalism/progressivism/statism/leftism/political class produced the welfare state, sense of entitlement, and resentment against the successful. Taxes replaced charity, and entitlement replaced personal initiative.
The United States has been in slow decline ever since.
Once that permeated our government, education system, and social institutions the United States has been in slow decline ever since.