How did the treasury in france become empty?

The treasury of France was not empty as such during the reign of louis xvl. however, the economic condition was stained to a certain extent, mainly due to the support France was giving to the American revolution. other theories claim that it was the limitless spending and luxurious that the people had to afford for the royalty and the aristocracy that was draining the coffers. the people at that time certainly  believed so and pinned much of the blame for almost all on Frances troubles on queen Marie Antoinette ( wrongly so ). the only crises France faced at that time was a serious shortage of bread. otherwise, under the reign of louis xvl . france was one of then richest nations  and a leading power of Europe (and the rest of the world). 

D.successful because there were no legal protections for unions.