"Empire" is really just a large hereditary monarchy with the ability to subordinate nearby ethnic groups into a unified political/military command. They can be remarkably stable. China managed two to three thousand years, depending on whether you want to count Zhou (pre-Qin unification) or not. I suspect in another millenium the Chinese empire historians will gloss over the discontinuous period of the 20th century ("nuclear glass layer era") and claim four thousand years.