So much for any theory that ethnicity, wealth, or low taxes are what makes happiness happen. The top scorer's a unique ethnic outlier, three are ex-colonial immigrant nations with large indigenous and unrelated minorities, one of the European ones has been a mixed nationality polyglot since forever, another can barely keep itself above water and only just managed to keep from being French or Spanish or Belgian, and the three (or so) Scandinavian countries (these days) have allied, coalesced, united and split up again too many times to count since the Ice Age and Vikings, and they're everywhere now anyway. Their people are relatively prosperous but hardly rich, and their taxes are all high.
But in all ten, the folks are all big on trade, talk, taking care of each other, not going to war, and are and way less scared of being called 'socialist' than, you know …