Here, star systems are connected with "wormholes". The wormholes facilitate travel at $250\ c$, regardless of mass. They are made using special ships. Any travel (including military vessels) not through the wormholes is well below light-speed (not more than $0.05\ c$, ).
It takes a road builder ship $50$ years to make each endpoint and $30$ years to make a light-year of "road". So, for example, to connect two systems $10$ light-years apart, a road builder ship takes $400$ years. A road cannot be constructed by more than 1 ship, not even by building from opposite ends. All of a road has to be built by one ship. Additionally, roads cannot intersect in the middle.
Here are some more information on the setting:
- FTL communication faster than the wormholes (at $10000\ c$) is available, but the transmission and reception equipment are too large for ships and are generally constructed on planets.
- The wormhole endpoints orbit the stars, and are indestructible and immovable for the purposes of this question.
- The possibility of simply making the trip without a wormhole remains.
- There are "countries" in this setup; a country contains around as many systems as there are cities in a real-world country.
- Two adjacent countries are generally connected (edge system(s) with edge system(s))
How would governments connect their systems, and how would connection treaties be made (i.e. how the adjacent countries connect their countries)?
I picture only few (one?) connection between adjacent countries, because then only one system has to be defended in case of an invasion.
Edits in response to comments
- A wormhole endpoint is an endpoint of only 1 road.
- A wormhole endpoint is 100 km in diameter and cannot be "turned off" (for the purposes of this question).
- Even in the roads, light travels at lightspeed, so incoming vessels cannot be detected early.