On the world scale Poland and Germany are in the same economic tier. The part that it will be messy, was actually what yourself said (so I didn't think you nee

On the world scale Poland and Germany are in the same economic tier. The part that it will be messy, was actually what yourself said (so I didn't think you need evidence for that). Well, one can also look at other models historically, if you think of a border as demarcation of the influence of a state. Historically China didn't have well defined border, the further away civilisations were vassal states which had to pay tribute (but received gift of higher value than the tribute, so the real tribute was acknowledgement of power). Another example would be afghanistan/Pakistan. The border is very transparent and at least in Afghanistan there is not a functioning government, but war lord tribal areas. But this is about border of state demarcation. The idea of people moving to other places is generally a new one (apart from earliest pre history or when masses do this, like in the migration period) new in the sense starting with colonization of the US.