The French had to hold off an enemy twice their size for three years in WWI. It destroyed the most productive parts of their country and to this day vast swathes of land are untouchable and poisoned*. It bled them dry while the Brits got their act together and the US twiddled its thumbs. Losing an entire generation tends to make things difficult 20-30 years later. Something like 1 in 3 French young men between the ages of 17-30 were killed, wounded or maimed. Their sacrifice saved us from a German dominated world.
Edit: Something else now that I am and able to think,
@BMAN, is, make no mistake, France won WWI. They took the brunt of the German onslaught, and they tore the heart out of the German Army. They led the Allied Forces and equipped it.
1) By the time the US had any meaningful number of troops on the ground in spring 1918, the French, with an assist from the Brits, defeated the Great Spring Offensive.
2) The French also defeated the Fall Offensives with some help from the US and the UK, but the majority of the troops were French, and most Allied forces (not the US) were under French command.
3) The French actually armed the US Forces as well as trained them.
4) Essentially, by the time the US entered the fray in numbers, the French, and the UK blockade, had already won the war. Germany could not win. The appearance of US Forces simply made it impossible for Germany to negotiate a favorable peace and expedited things by a year.
*
In the map below, the areas in red, to this day, are uninhabited because the soil is toxic from poison gas, and chemicals associated with explosives and there are tens of millions of unexploded munitions.