I hate the "America is Rome" argument/ example but it just isn't true or rather it oversimplifies Rome's mark on history and radically overstates America's. For America to equal Rome we'd have to essentially conquer 2 of the following 4: European Union, India, Russia, and China and we'd have the next 200 or so years to do it; we'd also have to take the additional steps of forcing a religion upon them and destroying or "modernizing" their cities to conform to American standards across the board. Razing buildings, temples, redesigning roads and the layout of the city, etc.
But the example is apt because of history. Most nations/ countries/ empires aren't "fortunate" to have a clean death like the Persians or Kwarazmians wherein a relatively strong and united nation was utterly crushed by outside forces. Rome, the Crusader States, the Mongols, Chinese dynasties, the Greek city-states, Alexander's Empire, and the Byzantines all "enjoyed" serious internal dissention and fighting prior to outside entities administering the killing blow. In every case trade was weak, the masses were angry, the people and government divided, and their armies weakened by it all; this all allowed for outside forces to get their plunder on. I'm sure if I did more digging I could find numerous European and Muslim examples over the course of the last millenia or so.
If you look at successful revolutions over the last 200 years, the same can be said for the above except that internal forces (the people or the army) deposed the government.
The English victory at Agincourt was in large part due to internal weaknesses with the French monarchy. The English failed to capitalize on their crushing victory and the French lived to fight another day.
To a lesser extent we could also cite the indigenous Americans who had they united against the Spanish would have destroyed the conquistadors. The Spanish capitalized on existing enmity within the various tribes/ people to win allies and weaken their opponents. In America tribes turned against other tribes and we used that to our advantage, decreasing the wars by a decade or two. Smallpox helped but Central and South America would be very different with or without it.
Dragging out the comparisons to Rome sounds great but most people tune it out; only a few will seize upon it. History has a long list of nations and empires which died as a result of their internal issues weakening them to the point that other forces could act upon them.
