Following the French Revolution in the 18th Century and the collapse of the European monarchies in the Code Geass timeline, European nobels had fled their homeland and fled to Britannia to seek refuge and saftey from persecution by the revolutionaries. Centuries later the Holy Britannian Empire has declared war on the EU and has invaded and conquered most of Russia. The former nobels now take it as an oppritunity to reclaim their lost land all those years ago and Euro-Britannia was founded in 2017 a.t.b. Founded and led by 21st century Britannian Nobels, they've set up a small sub-empire in the conquered territories in Russia and Turkey and now wage war against the EU and supporting Britannian military advancements into the continent of Europe. Seeking vengence for their lost land, they are armed with Britannian military technology and resources and now wage a military campaign to conquere mainland Europe.
Euro-Britannia is modeled after Britannia being an absolute monarchy. It is led by the Grand Duke Augusta Henry Highland as the Head of State and is assisted by minor Nobility.