Umm, hoss, France STOPPED the German invasion in World War I. Stopped it cold. That's why the Germans went into trench lines and tried to win by attrition (against a country with only half the population of Germany) what they couldn't win outright on the field.
Yes, in World War II the French were totally outmaneuvered, and lost as a result. But there was much more to that. Had the French any spirit to really fight the Germans in World War II, the result could have been quite different. Only Paris? SO WHAT. And fight on. Germany would have had a very difficult time actually subduing and occupying all of France had the French army remained in the field, fallen back, and continued to fight. They didn' The national morale failed completely, and that was BECAUSE OF the mass death of World War I. In World War I the French Army STOPPED the Schlieffen Plan. The German invasion FAILED. But France was so outnumbered that she could not win a war of attrition without British, and later American, help. The population differential was the key to the balance of power between Germany and France in World War I. German tactics were not appreciably superior, as the French DID stop the Germans, cold, and held them, as the two sides bled each other to death. With only half the people, France was going to bleed to death faster, and was so ravaged that the will to do it again, a scant 20 years later, with a reduced next-generation thanks to the war dead from the last one, was not there.
Population was the key, and France paid dearly in the 20th Century for zero population growth in the 19th.
Suppose, instead, that France had grown in the same proportions as the rest of Europe. The French would have outnumbered the Germans, and the Germans would not have dared attack them in the first place in 1914, let alone 1870.
Most of European history, during the long periods from the Middle Ages onward when France was the super-populous country, were the histories of various coalitions to stop the relentless expansion of the French Kingdom pressing on its borders. When the birth rate plummetted after the Revolution and the Napoleonic wars, France ceased to be the pressing threat, and it was the rising, rapidly expanding population of Germany that became the largest, and the menace to the peace.
Demography is destiny.
First, the German invasion of Belgium and France suffered from having to run two fronts since Austria-Hungary wasn't taking care of the Russians on the East. Having to commit massive troops to East Prussia, the German numbers available to fight on the West weren't much larger (if at all) than the French and British numbers.
Second, the initial French attacks were failures. Only two things kept the Germans from wiping out the French: the thought that the British wouldn't join the battle in significant numbers (and certainly not us joining), and ignoring the Schlieffen Plan.
In World War I the French Army STOPPED the Schlieffen Plan.
Rupprecht weakened it as he just did a straight counteroffensive against the then-entrenched French instead of digging with minimal troops while the strong north flank surrounded the French army. Even then, the plan almost worked, but the Germans marched to the East of Paris instead of along the Channel, exposing a flank. Still, the French Plan XVII was a complete failure, and they would not have survived if not for the British intervention. The British commanders were highly critical of the ineffectiveness of the French commanders -- they were actually worried that the uncoordinated French retreats (as they were wont to do) would expose their flanks.
The French had the people, they just had horrible commanders.
The French would have outnumbered the Germans, and the Germans would not have dared attack them in the first place in 1914
The combined Arab nations far outnumbered the Israelis in population and they lost, a few times.