It is my contention that the Royal Navy and the French Army won World War I. The Royal Navy were past masters at blockading, it is how they dealt with all continental wars in the centuries past and only the American Revolutionary War slipped past their grasp using this strategy. The British sea blockade and their halting of the German ability to source materials through neutral nations placed direct pressure on German ability to expand their war economy.

The French Army was important as it bore the brunt of the fighting and the largest amount of the front. The French ability to absorb the German offensive in March of 1918 and stop it from reaching Paris or the coast is what saved the allied cause. After that the German back was broken and the pressures of lack of manpower, materials and food all came together to collapse Germany's ability to conduct war.

William H. McNeil writes in The Pursuit of Power that France was also the arsenal of democracy in World War I.

Originally the allies thought the war would be over in a couple of months, so it was never intended as more than a short term emergency. The rapid stalemate into trench warfare, the horrific losses against fixed defenses especially machine guns, and the sheer scale of industrial warfare (it went through a lot of ammunition and shells daily) led to a rapid re-ordering of the economies in France, Germany and Britain.

France was in a double bind as their main heavy industrial region had been invaded by the German Army. France lost nearly 65% of its coal production, 25% of iron output and almost half of its blast furnaces. To add to the concern artillery was using massive amounts of ammunition daily. This led to the French government establishing emergency measures to meet that demand. Employers were allowed to search railway stations and other military and mobilisation gathering points for skilled workers and co-opt them into the economy.

Any manufacturing location was pressed into working toward the war effort initially and the inefficient and high cost producers were weaned out through centralised material allocations as French production capacity stabilised and began to meet demand.

A French built Spad XIII of the United States Air Service.

The loss of eastern France meant that old and established patterns of working were no longer present. So new innovative methods of working were introduced by both capital and labor. Additionally, because so many natural resources were lost, France imported what it needed from overseas as it needed, allowing the economy to expand far past the limitations of local resources. Though there were pressures on material allocations as the British economy warmed up in 1915 and the American economy in 1917.

McNeill writes:

Here too [artillery shell production, tanks and aircraft ie WWI high tech] France equaled or exceeded what the other great powers were able to accomplish, so much so that when the American Expeditionary Force began to arrive in France, most of its heavy equipment was, by arrangement, supplied from French factories and arsenals. France, more than Britain and far more than America, became the arsenal of democracy in World War I.