Earlier quoted context omitted.
Poetically, this universe you've created reminds me of the story of the Berlin metro during the Cold War. Prior to the division of the city, the metro system spanned the whole city, and was rebuilt to functioning capacity in the aftermath of WW II. Once it became necessary to construct a controlled border between the NATO and Soviet sectors, they eventually erected barriers on the tracks; creating two disconnected tr…
Were the armed guards there to keep the western trains from stopping or for keeping easterners from escaping via the tunnels?
Realistically, the guards were put there to halt the transfer of people, goods, and currency: to be the physical manifestation of a hard border. Although, the motivation for this border (who it benefits, is it to keep "others" out vs "us" in) was a dynamic concept that evolved over time.
However, if you integrate the motivation function over the entire time of separation, which is one way of reducing the complexity, the primary result is to keep easterners from escaping. In the early days of widening division, there was a mass migration of people fleeing "The East"; each person carried a multitude of reasons for their flight. One effect of the border was to halt this flow.
There were easterners who sincerely viewed this differently, and wanted to keep westerners out (especially the "spies"!); however, their perspectives were definitely a minority, and don't survive the integral.