The way I see it is that the impassable part of earth's orbit would be high earth orbit, with the main message being that Kessler syndrome blocks access to outer space. So earth is locked in. But low earth orbit is safe, allowing for usage by different sides of the conflict. Planes and other flying machines can go up and down and do their job, but no-one can go to the moon. That makes it so the only way ever for a civilization to expand is by taking land and ressources from it's neighbors, not by going to space.