Otherwise, if your subfolder only contains an index file (imagine the screenshot above WITHOUT the ..._subflder_content_page and ..._external_link), the url to this file will be something like, ..../navigation_item1/nav_item1_subfolder/index.html.
Instead you should simply use a content page directly under the navigation_item1 folder, so the url will be shorter, .../navigation_item1/nav_item1_subfolder.html, where nav_item1_subfolder is representative of the name of the file.
For example, the following shows an expanded top-level navigation folder (research) that contains only content files (no navigation subfolders).
Alternately, if subfolders had been used, there would be a current_studies subfolder containing only an index file. The corresponding url's would look like this:
With a Navigation Subfolder: ..../research/current_studies/index.html
Without a Navigation Subfolder: .../research/current_studies.html
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