That may be true, although there was no internet available to rapidly spread British culture to every last corner of the globe.

It does seem as though US cultural hegemony may be on the decline. I'm not convinced that we'll see the end of English as a global language though. It's universally used as the language of international business. Most software developers need to learn English in order to write code. I don't buy the idea that Mandarin will be the world's language within 50 years.