Code Geass

Code Geass: Lelouch of the Rebellion (コードギアス 反逆のルルーシュ Kōdo Giasu: Hangyaku no Rurūshu?), often referred to as simply Code Geass, is a Japanese anime series created by Sunrise, directed by Gorō Taniguchi, and written by Ichirō Ōkouchi, with original character designs by manga authors Clamp. Set in an alternate timeline, the series focuses on how the former prince Lelouch vi Britannia obtains a power known as Geass and decides to use it to obliterate the Holy Britannian Empire, an imperial monarchy and a superpower that has been conquering various countries. Read more here.

Super Robot Wars IO
In Super Robot Wars IO, Britannia was founded after the collapse of the United States of America during the Age of the Jaegers. They were used as a proxy by the secret organization HYDRA, to oppose the DRAUGR hegemony on the Euro-asian continent.