Domestic matters are inherently too complex to predict. Through my life I've known many long term happy couples with substantial cultural differences and seen a lot of divorced in ~5 years couples from similar backgrounds.
The US is definitely a more difficult place for the couple to be settling, though I know some there. I find European countries are simpler logistically in an absolute sense (not necessarily familiar to an American) and the average European who marries someone from a different continent is starting from more knowledge of intercultural complexity than someone in the US who doesn't really need much more than shallow awareness of other cultures.
The US is definitely a more difficult place for the couple to be settling, though I know some there. I find European countries are simpler logistically in an absolute sense (not necessarily familiar to an American) and the average European who marries someone from a different continent is starting from more knowledge of intercultural complexity than someone in the US who doesn't really need much more than shallow awareness of other cultures.