How did charlemagne gather together many of the former roman empire’s european territories

Charlemagne was able to gather together many of the former Roman Empire’s European territories by conquering many European kingdoms and fighting off invaders. He ventured out to different lands and invaded different cities and countries to be part of the Roman Empire.

i think it's a)sparta

social contract theory, nearly as old as philosophy itself, is the view that persons' moral and/or political obligations are dependent upon a contract or agreement among them to form the society in which they live