The famed marriages of Habsurgs to relatives usually was with cousins, if that. Charles V got his empire through inheritance, and the Habsurgs were not keen on everything moving too far apart. Though they did tend to use their relatives as dukes, governors, etc, but that isn't really on topic. Let's see... Why would the Habsburgs support this? Or Hapsburg-Lorraine, since the full-blood Habsburgs died off due to all the inbreeding. I feel that, even under orders from the Emperor, NO ONE would agree to an arranged marriage involving the past arranged marriages had failed because two people grew up with each other and thus were not sexually attracted to the other. Kind of gets into the whole thing with Sigmund Freud and his theories of an Oedipus complex, which happened to him (to an extent) because he had been raised through childhood by a nanny, and so his body/subconscious didn't recognize his mother as being his mother when... actually, this is getting too creepy to even finish the sentence of. If you feel discomfort reading that though, just imagine two people who knew each other through their lives, both as friends and siblings, and imagine their thoughts if someone said they should get married. Kinda like in the Lion asking, with Nala and Simba. I have some doubts they would have been attracted to each other quite as much if they grew up with each other, rather than knowing each other as kids, then meeting again as young adults.
