I spent a few years in the US, coming from Scandinavia. It took several months before I was able to navigate the whole "strike up a conversation with anyone"-thing. The issue wasn't so much being "forced" into conversations (which I got used to fairly quickly) as it was knowing when these interactions were considered over by the other party. I'd often, unintentionally, overstay my welcome. The general vibe and attitude were also quite different.

The biggest shock was however moving back home. I'm originally from one of the larger cities in my home country, but ended up in a tiny village through a series of coincidences. Going from a multi-million US city to a tiny Scandinavian mountain village was rough. Went from a place filled with outgoing people to a place where the cashier in the local store still took me for a tourist after having lived there for a year. An almost impenetrable society. I've been here for a decade now, and have long since realized that I will always be "that guy from XYZ". On the plus side, it's nice not having to deal with people beyond my own family an coworkers. On the negative side I have almost no sense of belonging here outside of my wife's family who are all local.