However, you could use some descriptive phrases to convey the idea of multiple empires:
* A constellation of empires
* A league of empires
* A collection of empires
* A grouping of empires
* A panorama of empires
You could also use more general terms like:
* A collection of powers
* A cluster of civilizations
* A world of empires
Ultimately, the best choice will depend on the specific context and the desired effect.