I would say all the countries in earth are interlinked in one way or another to each other all of them depend on each other in some proportion. The reason why any small happening in united States or Europe effect global market because these two economies are heavily connected working on a lot of leverage with many many different countries through which causes the dependence on global  markets. It is not about the united States of America or the Europe being saturated deveped economies it is just that these economies work with other small economies on a lot of leverage which brings a lot of volatity in the market place due to high leverage and high risk.