Do you know how a nomad is someone who doesn't have a permanent home and instead move around to find things they need like water, food, and shelter? Well, a nomadic empire is a group of people who are also nomads but they have an army and a leader that helps them conquer other places and control their people.
Imagine you and your family live in a big tent and move from place to place with your animals, but your group is so big and strong that other people are scared of you and listen to what you say. That's kind of what a nomadic empire is like.
In the past, some groups of people like the Mongols, who lived in the grasslands of central Asia, formed powerful nomadic empires. They were expert horse riders and used their skills to travel far, conquer other lands, and take over cities. They would usually form alliances with different tribes along the way and even marry their women, so they would gain more power and become stronger.
Eventually, these empires became really big and even had permanent settlements where they could store their wealth and keep their animals. But most of the time, they would still move around and conquer more land. It was like being a king and a wanderer at the same time!