What would you call the actions against German forces by Allied forces(excluding Stalin's men) prior to D-Day?
The Atlantic, and the skies of W-Europe, as well as the med. The greatest amount of blood drawn from the LW was not in Russia, and the situation in the med costed the Axis steadily growing resources as well as depriving them from stocking their armies from the black Sea.
Anyway, to the original topic of the war in France.
What the French learned correctly from WWI was that a well fortified front (trenches, strongpoints, arty) would take unbearable costs to overcome, - untill there was armour. So, they devised a front that would also stop armour, - the Maginot line.
The Germans however, learning the same lesson, devised an offensive plan, which utilized speed, combination of arms, and most importantly, flanking.
10-12th of May 1940 (approx). may have been the riskiest day in Germany's war, when Guderian took his armour through the Ardennas and into the lowlands. He basically drove through, while it was not known it would work so well. As it was to be proved later, getting through that area could be one painful ride.
So, had France co-operated better with Holland & Belgium setting up defences, things could have gone the other way....or at least quite differently.