That's because people hadn't experienced very much of other cultures.
At the Brussels Expo of '58 you had a Congolese village where the Belgians fed the African kids bananas.
http://www.radio1.be/hautekiet/foto-congolees-dorp-expo-58-gaat-de-wereld-rond

Also in the US. Immigrant policy favoured Northern Europeans and tried to limit the number of Southern Europeans. If it had been more specific they would have said England only.