There is no question that the US market is the hardest to break into. I believe that the reason for this primarily has to do with the fact that the majority of the most powerful radio stations in the US are owned by Clear Channel. They are massive and have the ability to break artists worldwide. For the most part, they are dealing directly with the major labels in the US, with whom they have had long relationships. If you are an artist that is not being pushed by Clear Channel radio in the US, your chances of becoming a household name are slim.