I mean even native american nations within the US have cultural differences.
I wish I had a metric to go by, like number of shared common past times, language, legal structures, life goals, etc.
Like China Town vs a minnonite community vs the bayou vs rual Midwest vs New York vs Atlanta vs Islanders vs Indians on the Res vs Inuits vs Cuban Americans vs Mexican Americans is just a awesome variety to me. I've had the pleasure working with people in all those places and it really destroys the notion of "common sense" because depending how you are raised it really changes what you think is common.
You do have the melting pot effect multiplied by living in the era of mass communication and rapid transport too. So one person maybe surprised that you having handled a rattle snake or wrestled a gator or shot a machine gun or gone surfing, but you can talk about what just happened on game of thrones or the news.