American culture is controlled by huge multinational corporations who therefore are well able to sell it all over the world. So yes you will find McDonald's, Subways, American movies, American brand clothes, etc... all over the world. It does not necessarily mean that 1/ THIS is american culture or 2/ that american culture has taken over these countries cultures.
If you take movies for example, yes Hollywood movies sell everywhere, but there also very popular local movies. In France for example, Titanic's all time records of cinema entries has been broken last year by a French movie: Bienvenue chez les Cht'is. The UK has many world famous actors, like Judi Dench, Emily Blunt, Catherine Zeta-Jones, Michael Caine, Kate Winslet, Hugh Grant, etc... and have particularly successful with comedies (Love Actually, The Boat that Rocked, Four weddings and a funeral, etc...).
Not to mention the general mentality and way of looking at things always remain very different.