As B2C site does requires the user to have an existing account and ability for any user to create an account on the site while placing an order makes it difficult to restrict a user from another country to place an order on any B2C site. There is a work around that you can use to restrict the user from another country to place an order on you site. You can create a non-integrated shipping method based on country. The shipping method is called as “Non-Integrated Shipping Zone”. In this method you can list the name of your country and select this method as the only shipping method for your site. This method will restrict the user from placing the order unless they will have the name of the country in their address.