For all the talk of British action, the British Expeditionary Force was a damp squib. The Island kingdom could stand back and let the French face off against the Germans (no cowardice -- this made sense as the Brits did not have enough soldiers -- their's was a professional army while the French and German armies had conscripts. The Brits would have wasted professional soldiers on this and they were better served elsewhere)
The Russians were fighting in their own war with the Austro-Hungarians and Germans on the Eastern Front, and couldn't spare help for Verdun.
The Italians joined in 1915 and this war was primarily against Austro-hungary, against whom the Italians had a border (no border with Germany)
Remember that Germany's aim in WWI was to quickly defeat the allies in Western Europe, settle a treaty and then attack the Russians
The French saved Western Europe because at that time, the Brits did not have the numbers to stop the Germans and the US was too isolationist to enter in the effort. If France had fallen in 1916, England would sign a treaty (remember the King and Kaiser were both grandsons of Queen Victoria) and the Russians would have been shortly dealt with. The French stand at Verdun "Thou shalt not pass" On ne passe pas
Verdun was planned as a vehicle for destroying the French Army.
on other points, Germany wasn't a unified country yet in 1805, but they had a strong, Spartan-like military state in Prussia that was swept aside and a huge empire in the Holy Roman Empire. The armies were as unified as anything on the continent, but they were all defeated by France.
Ditto for the 1600s when these patchwork of nations was still theoretically united under the Holy Roman empire.
France is not cowardly and it is wrong to just take their actions in 1941 to overwrite 1500 years of history. If anything, they are too quick to action -- stupid action that harms Western civilisation as a whole, but still action. Even 1941 can be understood in the context of the bleeding they suffered in 1914-1918 and the fact that much of the wars of the trenches, the millions dead were on French or Belgian soil