Americans may not think of themselves as an “empire,” but much of the world does. The average age of empires, according to a specialist on the subject, the late Sir John Bagot Glubb, is 250 years. After that, empires always die, often slowly but overwhelmingly from overreaching in the search for power. the US is 249 years old.
Some argue that all organizations, including governments, eventually become oligarchies. See The Iron Law of Oligarchy (1911)