Amazon.com makes almost $45 bn per year in sales. However, Amazon Germany made over $10 billion in 2013 and Amazon UK made over $7 billion. Once you have success in Amazon USA, it’s time to consider Amazon Europe.
You can sign up for an Amazon Seller Central account in Europe.
http://services.amazon.co.uk/faq-for-the-amazon-europe-marketplaces-account.html