Oh and, as to how the empire could have come about; perhaps there was a giant concentration camp hidden away in Canada? Towards the build up to the war, Vault Tech and the US government were not only locking away communists, but also people of Chinese descent. 

When the bombs fell, the camp could've fallen into a state of disrepair and the inmates, now very much anti capitalism, could have repurposed the facility as a sort of base. Fast forwards two centuries, and you have the Tinsui.