Modern web site software - like Drupal - simply provides a web-based front end to a database. For a traditional web site, the front end retrieves articles and formats them on HTML pages. A more sophisticated web site allows more sophisticated access to the database.
If we embrace this vision, we build a new web site by importing databases. On Drupal, that means we use the Feed Importer. I have finally gotten the Feed Importer to work, after several hours of banging around.