Empires are a pretty durable and effective cultural unifiers. Most people on Earth speak the language of one or more empires (English, Chinese, Arabic, Spanish, French, German and so on). Many of these languages, like the romance languages, have been processed through multiple empires. But empires, like other products of man, are mortal. Rarely do they perish solely or mainly from revolt of the subjugated. Usually they fall victim to other empires or the internal struggles of the central elite.
It's possible that the current convulsions in Washington signal the end of America's preeminence in the world. there is little doubt that they have done grevious damage to the country. It could turn out that one Cuban/Canadian terrorist and his allies do more damage to America than bin Laden and al Quaeda ever could.