The British royals visited Jugoslavia and it was a country known in the UK. To be honest British schools should introduce Europe Studies classes and instead of teaching US history they should teach the history of European countries, including Slavic ones.

The Brits don't have Euro studies classes in schools, really? How strange. In Canadian schools we learn about the history / culture of the following – Canada, Britain. France, Russia, Germany (all of those in detail)
Ancient Rome, Ancient Greece (in detail)
At least the basics about Italy, Ireland, "Eastern Europe", the USA, Japan, a bit about Ukraine, Poland
And, of course, about most regions of the world – at least a basic intro/history of nations of Africa, Middle East, Asia, South America, Australia, etc.