You can definitely cherry pick some examples for that to be the case, particularly for historical reasons and/or very close cultural ties. From an outsiders perspective, Austria and Germany are extremely similar (though neither Austrians or Germans would tend to agree!)

Whilst cultural differences in the US do undoubtedly exist, in Europe simply travelling a hundred miles can take you across 3 countries with 3 languages and 3 distinct cultures. There's plenty of diversity to be found.