There is much more that can be said about this, but you might like to see a reply by /u/Aleksx000 at "When the idea of French military weakness become popular?" . One important bit is referred to by /u/DuxBelisarius at "When/how did France acquire its reputation as a nation with an embarrassing military history?" .

For World War II specifically, /u/kieslowskifan replied at "I've heard that the French lost the Battle of France in WWII largely because they didn't want to fight. Is that because they were Nazi-sympathyzers or pacifists?" .

Mentioning previous results is not to discourage discussion. More questions, data, and debate are welcome.