All nations and empires rise then decline and fall.
America rose on the back of the pioneers and the huge resources found in many parts of the states.
Most of those resources are in mid to late decline. and America has only been able to continue to grow on the back of Hitech advances.
Traditional Industries are in terminal decline, and the millions who depended on them have in the main had to settle for lower paid alternatives.
Education for the masses, which never advanced much above the basic, has been over taken by many third world countries; and has been eclipsed by India and china, Japan and other eastern countries.
American prospects are not yet hopeless, but will take a major change in attitude and thinking.
The individualist approach which have served them well in the past, no longer works well in the crowded modern world. America must learn some of the co-operative benefits of socialism...especially regarding health care, education, insurance, and government lead investment where people rather then profit are the main motivator.
Unless America Does this, the social pressures that in the past have been a source of strength, will start to tear her apart. Then she will truly be on the downward trail.
For many generations she is likely to be an important Country, But like the UK will have here best days behind her. The dominant countries of the future will see America, a debtor nation, as a vast land resource that they can exploit. The American People will be used in this exploitation, as an almost inexhaustible supply of local cheap labour.