At least until 1934, the Ardennais Chasseurs were supposed to make a fighting retreat and occupy the Meuse line between Givet and Dinant. Even before 1936 there no plans to fortify that portion of the river. The main Belgian Army would focus around Liege and the Dutch border (5 active, 3 reserve, 1 cavalry division just to face the flank in the Dutch border). So, they expected the French to cover most of the rest of the line. In that light, it makes even more sense for Sedan to become a fortress, since they would expect to send field formations north to Namur and the Meuse that won't have protection by modern fortifications.
Makes sense.
On the French side, four options were studied, the last three involving war on Belgium territory
- option 1 screw Belgium, fight the Germans on the frontier
- option 2 enter Belgium up to Escaut river, fight the Germans there
- option 3 enter Belgium deeper, up to river Dyle
- option 4 "hey, once at Dyle, we are not that far from the Netherlands... how about pushing to Breda ?" this way, we defend a second democracy, The Netherlands plus Belgium
guess what option was picked up in March 1940 ? the Breda one,except it took one more army, a very mobile one, to rush to Breda, bury there, and awaits the Germans.
Of course it was General Giraud army, the 7th army, that was send there... and moved out of Reims, where it was the strategic reserve to crush a possible german breakthrough the flatlands - Gembloux, Namur. Or through the Ardennes - no, I'm just kidding (bangs my head against a wall).
What is completely nut/ insane, in retrospect, is that the (fatal) slide from option 1 to option 4 happened between October 1939 and March 1940 ! Because politically, it become impossible for France to gave up the Netherlands... another reason, in retrospect, to hang Gamelin by his testicles, for utter siliness...
General Giraud has been badly treated by history because he lost the Free French to De Gaulle (and also because Giraud, really, was a little dumb).
But Giraud made one hell of WWII.
On May 10 - 11 he rushed from Northern France to Breda, across the entire northern Belgium, with its 7th army which was acclaimed by people.
Only 6 days later having rushed back to northern France in the wake of Sedan, he was stupidly taken prisonier while trying to catch pace with a German army that simply moved too fast.
18 months later he evaded like a true badass from Colditz where he was held prisonier, told Vichy France to go fuck themselves, entered La Resistance, was exfiltrated to Free French territory. And then there was the entire political struggle with De Gaulle (and Roosevelt, his ally).
All this, with a bad limp inherited from a bad horse fall during the interwar.
The fate of General Henri Giraud in WWII is really a mirror of what France endured during the war.