When the Roman Empire was expanding, the Romans received some pushback when they arrived in Britain. Celts were already there, and they weren’t going down without a good fight! We studied this in history and then made axes, dressed up and had a couple of battles. I was a Roman trying to conquer Britain. The girls were Celts, fighting against me. Eventually, the girls fought against each other because, as they learned, the Celts (various tribes) fought one another just as often as they fought outsiders.
And did you know that one Celtic king / warlord (Vortigern) eventually got tired of fighting his Celtic neighboring tribes, so he went across the North Sea to find people to help him fight with him?. The two groups of people he requested help from were the Angles and the Saxons. Vortigern promised them land in exchange for help fighting. The Angles and Saxons liked Britain so much that they did stay and invited their friends to come too, eventually moving most of the Celtics out of the area (and into the area we know now as Wales, Scotland, and Ireland). The Angles and the Saxons stayed in the area we now call England, and this is why people from this area were/are often called Anglo-Saxons. Do you hear my enthusiasm? I totally just learned this with my girls!