[sofixa]

Belgium and the Netherlands and Luxembourg were the same country, at least for some time, then split up and are good countries to live in (probably beating the US on most quality of life metrics). Same goes for the Nordics which were at different times in various combos (Denmark-Norway, Sweden-Finland, Sweden-Norway, Iceland was a part of Denmark).

Also a bunch of other examples where the countries aren't necessarily the best to live in, but pretty much everyone is happy they split - Yugoslavia, India/Pakistan, West Pakistan/East Pakistan. Singapore/Malaysia (to be fair Singapore were kicked out).

A split of the US among the crazily politicised duopoly wouldn't be the end of the world. One part would be reactionary as hell and move time back (on social and ecological issues), the other.. who knows.