Why do you have to dress appropriate to the culture overseas, but foreigners bring their dress-code with them?

Well first America is more evolved than other countries so we respect all religions and customs here. While in other countries their laws abide differently than ours. They want to preserve their culture and since those countries have more natives living there it's easier to keep them. Our country consists of different nationalities from all over the world. It would be hard to base this country off one culture and follow that. While other countries mostly have their own people living in it.