This all the way; the co-princes system can be used as a rudimentary federal system.You mean Franco-Spanish union isn't automatically MegaAndorra?
Does anyone want to help me come up with a flag for a First French Empire in a union with a Spanish Empire? Preferably something simple that revolves around color, not symbols. Both countries are ruled by the Bonaparte Family.
It's a bit convoluted, but how about this?
Second version with two intersecting French flags