A big river like the Rhine is usable as a border because it is absolutely a natural border easily defended for an army. Both armies come from their respective capitals and don’t really care that the towns on both sides are friends and have deep cultural and economic ties. They only care how easily they can dunk on the soldiers or barbarians as they are waddling through the water, or funneled on a bridge.
The frontier is where you can guarantee protection with your army. If you can’t cross the river fast enough to stop raids on the town on the other side, then it’s not guaranteed protection, and it’s not part of your country.
Alsace/Elsass kept changing hands between Germany and France back and forth for hundreds of years. The Rhine is a good defensible position, which might be why the area that kept changing hands wasn’t extended to Baden, Württemberg etc., but evidently not good enough to prevent the existence of German populations west of the Rhine.
A big river like the Rhine is usable as a border because it is absolutely a natural border easily defended for an army. Both armies come from their respective capitals and don’t really care that the towns on both sides are friends and have deep cultural and economic ties. They only care how easily they can dunk on the soldiers or barbarians as they are waddling through the water, or funneled on a bridge.
The frontier is where you can guarantee protection with your army. If you can’t cross the river fast enough to stop raids on the town on the other side, then it’s not guaranteed protection, and it’s not part of your country.
Alsace/Elsass kept changing hands between Germany and France back and forth for hundreds of years. The Rhine is a good defensible position, which might be why the area that kept changing hands wasn’t extended to Baden, Württemberg etc., but evidently not good enough to prevent the existence of German populations west of the Rhine.