Analyze how changes in the United States have led to problems for the U.S. as an actor on the world stage.
This is an excellent question. You are right in intimating that what happens here has a direct effect on global politics.
Arguably the best example of this is in the area of banking.
In 2008 our financial system crashed. What seemed like an impossibility happened. Lehman Brothers went down. Merrill Lynch, AIG, Freddie Mac, Fannie Mae, and others all came within a half-step of collapsing as well. All of this showed two things.
First, American greed had finally taken a toll. Americans could not spend their way to growth. The world realized that America was the greatest debtor nation in the history of the world. What seemed solid was far from it.
Second, what happened in America affected the rest of the world. If we defaulted, then other nations would not get paid or paid little. If we inflated our way out, then others would get less. In the end, America was no longer the only country to propel growth. China could now also be seen as a mover and shaker in the financial world. Many countries now are more apt to seek opportunities with China than America. This is now the new state of affairs.