Question

which two empires ruled at the same time for a few years ?

Answer 1

Empire of Japan: minimum 1743 years to date (see above)

Byzantine Empire: 874 years (uninterrupted from 330 to 1204)

Holy Roman Empire: 844 years (962-1806)

Zhou Empire: 790 years (1046–256 BCE)

Ethiopian Empire: 666 years (1270-1936)

Khmer Empire: 629 years (802–1431)

I hope this helped :)