Seems to me like it's about the couples transcending national borders, and starting to create a "European" identity rather than national identities.

Now I’ll be that person: Europe is not the monolith Americans imagine it to be. It’s roughly 50 countries and an equal (if not higher) amount of languages.

tldr; Europe is not like having 50 states in the US but each state has their own language, history, culture that can be very different from others.

Culturally, as a German I don’t have a lot of in common with a Polish or a French person. There may be things we can agree on, but eventually you being European is equal to being North American. The USA and Canada are probably kinda close to each other because of the mostly shared language. But then e.g. Mexico has a completely different history and language than those two.

And now add to that that Schengen came to effect like what 25 years ago. Before that there were border controls between EU countries. For people above 40 they still grew up with their world ending at their country’s border. Only in the last 15 years with open borders & cheap flights it became affordable to most to visit other countries.

Also, education, legislation, hell even on which side of the road you drive differ from country to country. There really isn’t that much that most countries have in common. So it’s very different than the USA. Or more like the difference between France and Germany is at least as big as the difference between culture in the Bay Area and rural Alabama. And also they speak a different language and most older people can’t communicate with each other all.

Erasmus is an European program for students exchange. I guess the people in this poster started a family like that