[Strengthandhonour]

This are all very interesting. The biggest problem in Europe, in my eyes is the negative birth rate. Invaders can be kicked out, but when they could out number you in a few decades it could become a problem which would end in the complete demise of Europe as we have known it up until today. One obviously cannot keep foreigners completely out of the country(embassys would still be required for diplomatic reasons and also trade relationships)
As it was stated, one cannot tell someone who to marry BUT you can make them lose their citizenship,etc if they marry someone different. The entire cheap labor is a worldwide phenomenon, not just something that takes Europe by storm. In many countries worldwide this problem is there, and it's not always countries with an European population but also in central and south america, often people from poorer countries go to the richer ones for jobs.
A huge reform must take place first in order for some of this things to take place, and one also has to remember that there will possibly be oposition if this is to take place.