The phrase "mighty empire" refers to a powerful and strong civilization or nation that has a significant influence and control over other territories and people. Full definition
Rise & Fall: Civilizations at War is a detailed real - time strategy game that lets players completely command one of the four mightiest empires of the ancient world: Greece, Rome, Egypt, and Persia. (megagames.com)
It's a question that will be familiar to players of the computer game Civilisation in which lowly tribes can become mighty empires. (newscientist.com)
War and unrest, and the collapse of many mighty empires, often followed changes in local climes. (newscientist.com)